Browsing by Author "Gadd, PS"
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- ItemAnomalous tree-ring identification facilitated by AMS 14C analysis in subtropical and tropical Australian Araucariaceae samples enables development of a long-term, high-resolution climate reconstruction(Australian Nuclear Science and Technology Organisation, 2021-11-17) Haines, HA; Palmer, JG; Hua, Q; English, NB; Hiscock, W; Turney, CSM; Marjo, CE; Gadd, PS; Kemp, J; Olley, JMIn Australia the majority of tropical and subtropical regions lack long-term instrumental climate records. Paleoclimate reconstructions from tree rings provide one alternative but very few dendrochronological investigations have so far been undertaken. Early assessments of mainland Australian tree species were discouraging due to the high prevalence of anomalous ring boundaries. Some species, however, were seen as more favourable than others including those in the Araucariaceae family which is common along the subtropical-tropical Australian east coast. These trees are longer lived than many other species in the region and contain growth rings known to be annual in nature and responsive to climatic conditions. There is however, a heavy prevalence of anomalous ring boundaries in species from this family which must be accounted for when dating these species. Here we describe the tree-ring characteristics and growth response from two stands of Hoop pine (Araucaria cunninghamii) trees located in subtropical and tropical Queensland, Australia (regions known for experiencing extreme hydroclimatic events). Confirmation of annual growth driven by moisture sensitivity was determined using radius dendrometers on four trees in Lamington National Park (c. 28º S). Tree cores were collected from both the Lamington stand as well as a stand at Hidden Valley near Paluma, Queensland (c. 19º S). Ring-width assessment showed the presence of false, faint, locally absent, and wedging rings in both sites. Results of bomb-pulse radiocarbon dating of selected single tree rings demonstrated that trees from this species can fall into one of three categories: A – those with locally-absent rings around the circumference of the trees, B – those where false rings were observed, and C – those with many wedging and locally-absent rings. Only trees in the first two categories were able to be included in the master chronologies. Traditional dendrochronological analysis with age validation by bomb-pulse radiocarbon dating allowed for a robust ring-width chronology from 1805-2014 CE to be developed for the Lamington National Park site. Growth-climate analysis of the master tree-ring chronology determined that the strongest environmental correlation was to wet season drought conditions. The strength of this response was compared to local and regional drought indices as well as to a long-term drought reconstruction. The combined analysis led to the development of a 200-year drought reconstruction for the region which shows influences from both the El Niño Southern Oscillation and the Interdecadal Pacific Oscillation. © The Authors
- ItemAnother piece of the Southern Hemispheric puzzle: developing a high-resolution climate record for multiple glacial cycles in eastern Australia(International Union For Quaternary Research (INQUA), 2015-08-01) Kermode, SJ; Shulmeister, J; Mueller, D; Goralewski, J; Gadd, PS; Chang, J; Heijnis, H; Cohen, TJUnderstanding likely climate change and subsequent environmental responses is critical to our long term ability to manage and mitigate such changes. Investigations of previous responses to notable (either abrupt or large scale) climate change provides boundary conditions and targets that can be used to both validate and parameterize the climate models used to predict future change. High-resolution records from the Southern Hemisphere lag considerably behind available data from the Northern hemisphere, and are particularly sparse in Australia. Given that most (>80%) of Australia’s population, industry and agriculture lie in the mid-latitudes between Southern Queensland and Tasmania, one might expect that past climate changes from this region are well understood, but this is not the case. Long, high resolution records are needed to address this gap. An 11 m core has been collected from a permanent swamp/lagoon (Mountain Lagoon), in the Blue Mountains west of Sydney, which appears to span at least one complete glacial cycle. This is potentially the most continuous record recovered from this part of SE Australia. Much of the record is at least moderately organic and preliminary sedimentary and Itrax data indicate that significant environmental changes are recorded. Multi-proxy investigations including pollen, diatoms, charcoal and phytoliths are planned and the chronology will be underpinned using OSL and radiocarbon dating. The focus of the investigation will be to develop climatologies for the Sydney region during the last glacial cycle. The Mountain Lagoon project will consequently contribute to understanding how climate systems in SE Australia respond to large scale global change on Milankovitch time scales. By determining the climate response in Australia to these changes we will help predict future response in rainfall and temperature to human-induced and natural climate change.
- ItemThe application of x-ray fluorescence core scanning in multi-element analyses of a stratified archaeological cave deposit at Wee Jasper, Australia(Elsevier, 2017-06-06) Theden-Ringl, F; Gadd, PSArchaeological sediments retain elements from natural and anthropogenic inputs for many years, often forming stratified geochemical records of site formation and human use. This study evaluates the validity and potential of an X-ray fluorescence core scanner (XRF-CS) to contribute to the histories of stratified archaeological sites. Geochemical data sets from an archaeological deposit at Wee Jasper in southeast Australia are obtained using two sediment preparation techniques; the results are compared to trends identified through cultural artefacts and several more traditional methods of sediment analysis. Potential anthropogenic and organic element signatures are identified, and the sediment preparation techniques are evaluated. Minimally processed bulk samples provide consistent XRF results that strongly correlate with the trends observed in other proxies; results from unprocessed sediment columns, however, reveal methodological complications with the XRF-CS technique due to topographical and structural inconsistencies in the columns. © 2017 Elsevier Ltd.
- ItemThe archaeology of overburden: method within the madness at ˇSv´edův Stůl, Czech Republic(Elsevier, 2021-08-01) Wright, D; Hughes, PD; Skopal, N; Kmošek, M; Way, A; Sullivan, M; Lisá, L; Ricardi, P; Škrdla, P; Nejman, L; Gadd, PS; Nývltová Fišáková, M; Mlejnek, O; Králík, MIn the 19th and early to mid-20th centuries, a rush to better understand the European Palaeolithic led to the substantive removal of deposits from limestone caves. In the 21st century the situation has changed. Many caves are now excavated, leaving behind a human-made environment of diminished cave sediments and large spoil heaps, with the latter now targeted by those searching for artefacts missed during the original excavations. In an age in which archaeologists are increasingly attempting to balance their roles as cultural heritage educators and destroyers, the question remains - how much do we know about the taphonomy of these features? In this paper we report results from the excavation of a large spoil heap outside Švédův Stůl Cave, in the Moravian Karst region of Czech Republic. Results show heterogeneous sediment formation (revealed primarily through their field characteristics and ED-XRF and Itrax geochemical analyses) and patterns in artefact distributions (evident through assessment of Iron Age, Neolithic and modern artefacts) and faunal remains. This allows partial context to be provided for some artefacts and a methodology to be developed for excavation of overburden. © 2021 Elsevier Ltd.
- ItemBiogeochemical responses to Holocene catchment-lake dynamics in the Tasmanian World Heritage Area, Australia(American Geophysical Union, 2018-04-30) Mariani, M; Beck, KK; Fletcher, MS; Gell, PA; Saunders, KM; Gadd, PS; Chisari, REnvironmental changes such as climate, land use, and fire activity affect terrestrial and aquatic ecosystems at multiple scales of space and time. Due to the nature of the interactions between terrestrial and aquatic dynamics, an integrated study using multiple proxies is critical for a better understanding of climate- and fire-driven impacts on environmental change. Here we present a synthesis of biological and geochemical data (pollen, spores, diatoms, micro X-ray fluorescence scanning, CN content, and stable isotopes) from Dove Lake, Tasmania, allowing us to disentangle long-term terrestrial-aquatic dynamics through the last 12 kyear. We found that aquatic dynamics at Dove Lake are tightly linked to vegetation shifts dictated by regional hydroclimatic variability in western Tasmania. A major shift in the diatom composition was detected at ca. 6 ka, and it was likely mediated by changes in regional terrestrial vegetation, charcoal, and iron accumulation. High rainforest abundance prior ca. 6 ka is linked to increased terrestrially derived organic matter delivery into the lake, higher dystrophy, anoxic bottom conditions, and lower light penetration depths. The shift to a landscape with a higher proportion of sclerophyll species following the intensification of El Niño-Southern Oscillation since ca. 6 ka corresponds to a decline in terrestrial organic matter input into Dove Lake, lower dystrophy levels, higher oxygen availability, and higher light availability for algae and littoral macrophytes. This record provides new insights on terrestrial-aquatic dynamics that could contribute to the conservation management plans in the Tasmanian World Heritage Area and in temperate high-altitude dystrophic systems elsewhere. ©2018. American Geophysical Union
- ItemCentennial-scale trends in the Southern Annular Mode revealed by hemisphere-wide fire and hydroclimatic trends over the past 2400 years(Geological Society of America, 2018-02-15) Fletcher, MS; Benson, B; Bowman, DMJS; Gadd, PS; Heijnis, H; Mariani, M; Saunders, KM; Wolfe, BB; Zawadzki, AMillennial-scale latitudinal shifts in the southern westerly winds (SWW) drive changes in Southern Ocean upwelling, leading to changes in atmospheric CO2 levels, thereby affecting the global climate and carbon cycle. Our aim here is to understand whether century-scale shifts in the SWW also drive changes in atmospheric CO2 content. We report new multiproxy lake sediment data from southwest Tasmania, Australia, that show centennial-scale changes in vegetation and fire activity over the past 2400 yr. We compare our results with existing data from southern South America and reveal synchronous and in-phase centennial-scale trends in vegetation and fire activity between southwest Tasmania and southern South America over the past 2400 yr. Interannual to centennial-scale rainfall anomalies and fire activity in both these regions are significantly correlated with shifts in the SWW associated with the Southern Annular Mode (SAM; atmospheric variability of the Southern Hemisphere). Thus, we interpret the centennial-scale trends we have identified as reflecting century-scale SAM-like shifts in the SWW over the past 2400 yr. We identify covariance between our inferred century-scale shifts in the SWW and Antarctic ice core CO2 values, demonstrating that the SWW-CO2 relationship operating at a millennial scale also operates at a centennial scale through the past 2400 yr. Our results indicate a possible westerly-driven modulation of recent increases in global atmospheric CO2 content that could potentially exacerbate current greenhouse gas–related warming. © 2021 Geological Society of America
- ItemChanges in biomass burning mark the onset of an ENSO-influenced climate regime at 42°S in southwest Tasmania, Australia(Elsevier, 2015-06-15) Fletcher, MS; Benson, A; Heijnis, H; Gadd, PS; Cwynar, L; Rees, ABHWe use macroscopic charcoal and sediment geochemistry analysis of two proximal upper montane lakes located at 42°S in southwest Tasmania, Australia, to test the role of the southern hemisphere westerly winds (SWW) and the El Niño-Southern Oscillation (ENSO) in governing the climate of this sector of the southern mid-to high-latitudes. Inter-annual climate anomalies in the study area are driven by changes in both ENSO and the Southern Annular Mode (SAM - an index that describes seasonal to decadal shifts in the SWW), making it an ideal location to test assumptions about the varying influence of the SWW and ENSO, two important components of the global climate system, through time. We find multi-millennial scale trends in fire activity that are remarkably consistent with trends in hydroclimate reconstructed at the same latitude in southern South America, providing empirical support for the notion of zonally symmetric changes in the SWW governing the climate at this latitude in the Southern Hemisphere between 12 and 5 cal ka BP. A transition from multi-millennial scale to sub-millennial scale trends in fire activity occurs after ca 5 cal ka BP in concert with the onset of high frequency and amplitude ENSO variability in the tropical Pacific Ocean region. We conclude that the onset of sub-millennial scale trends in ENSO drove changes in fire activity in our study region over the last ca 5 cal ka. Geochemical data reveals divergent local impacts at the two study sites in response to these major climate transitions that are related to local topography and geography. © 2015 Elsevier Ltd.
- ItemChanges 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, ANew 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.
- ItemChronostratigraphy of a 270-ka sediment record from Lake Selina, Tasmania: combining radiometric, geomagnetic and climatic dating(Elsevier, 2021-03-01) Lisé-Pronovost, A; Fletcher, MS; Simon, Q; Jacobs, Z; Gadd, PS; Heslop, D; Herries, AIR; Yokayama, YLake sediment archives covering several glacial cycles are scarce in the Southern Hemisphere and they are challenging to date. Here we present the chronostratigraphy of the oldest continuous lake sediment archive in Tasmania, Australia; a 5.5 m and 270 ka (Marine Isotope Stage 8) sediment core from Lake Selina. We employ radiometric dating (radiocarbon and optically stimulated luminescence) and relative dating (geomagnetic and climate comparisons). Bayesian modeling of the radiometric ages reaches back to 80 ka (1.7 m) and relative dating using a dynamic programing algorithm allows dating of the full sequence. Elemental data, magnetic properties and beryllium isotopes from Lake Selina reveal a close fit to Antarctic ice core climate proxies. Weaker correlation during the Last Glacial Period (MIS 2–4) is attributed to additional local factors impacting Lake Selina proxies at a time of climate changes and human arrival into Tasmania. Over that period, full vector paleomagnetic records and authigenic 10Be/9Be ratios are combined to identify the Laschamp geomagnetic excursion for the first time in Australia and constrain the chronology. The multi-method approach provides two preferred age models, indiscernible within their uncertainties, which allows the use of a geomagnetic dipole-independent (full archive) or a climate-independent (111 ka to present) age model. © 2021 Elsevier B.V.
- ItemChronostratigraphy of sediment cores from Lake Selina, southeastern Australia: radiocarbon, optically stimulated luminescence, paleomagnetism, authigenic beryllium isotopes and elemental data(Elsevier B. V., 2022-06) Lisé-Pronovost, A; Fletcher, MS; Simon, Q; Jacobs, Z; Gadd, PS; Herriers, AIR; Yokoyama, YThis Data in Brief paper comprises dataset obtained for sediment cores collected from Lake Selina, located in the West Coast Range of Tasmania, Australia. Datasets include radiocarbon and optically stimulated luminescence age estimates, elemental composition, beryllium isotopes, magnetic properties and the paleomagnetic record measured on the cores assigned as TAS1402 (Location: Tasmania, Year: 2014, Site number: 02). The multi-proxy dataset was used to develop a chronostratigraphy for the 5.5 m and 270,000 year old record. See Lisé-Pronovost et al. (2021) (10.1016/j.quageo.2021.101152) for interpretation and discussion. The data presented in this study serve as an archive for future studies focusing on Earth system dynamics and the timeline and linkages of environmental changes across Tasmania, the Southern Hemisphere and at a global scale. 2022 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND licence.
- ItemThe climate reconstruction potential of Acacia cambagei (gidgee) for semi-arid regions of Australia using stable isotopes and elemental abundances(Elsevier B.V., 2017-01-01) Witt, GB; English, NB; Balanzategui, D; Hua, Q; Gadd, PS; Heijnis, H; Bird, MITo provide multi-centennial, annually-resolved records of climate for arid and semi-arid areas of Australia it is necessary to investigate the potential climate signals in tree species in this large region. Using a stable isotope and x-ray fluorescence approach to dendrochronology in Acacia cambagei, this study demonstrates short (10 years) proxies of temperature and precipitation are possible. Because rings in A. cambagei are difficult to see, precluding traditional dendrochronology, we used elemental abundances of Ca and Sr as an annual chronometer back to 1962. Radiocarbon analysis confirmed that our dating of wood from two trees. We compared δ13C and δ18O from the α-cellulose of the dated wood over the most recent 10 years (n = 10) to local climate records demonstrating significant relationships between δ18O and precipitation (r = −0.85, p < 0.002); mean monthly maximum temperature (r = 0.69, p < 0.03); and drought indexes (CRU scPDSI 0.5°, r = −0.89, p < 0.001) for February and March. Acacia cambagei may be useful in developing regional networks of climate proxies for drought. Using modern trees, in combination with architectural timbers, it may be possible to construct a multi-century, annually-resolved proxy-record of rainfall and temperature for semi-arid north-eastern Australia. © 2016 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
- ItemCoherent 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, SKAt 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
- ItemCombined use of stable isotope analysis and elemental profiling to determine provenance of black tiger prawns (Penaeus monodon)(Elsevier, 2019-01-01) Gopi, K; Mazumder, D; Sammut, J; Saintilan, N; Crawford, J; Gadd, PSGlobal demand for seafood is rising, with a commensurate increase in supply from farmed and wild-caught products. Determining seafood provenance is important to reduce food fraud, and food safety and biosecurity risks. DNA and fatty acid profiling cannot independently distinguish between farmed, wild-caught and geographic origins of seafood. This study applied stable isotope analysis (SIA) and X-ray fluorescence (XRF), using Itrax, to test their effectiveness as tools to distinguish the origin and production methods of black tiger prawns (Penaeus monodon) from a range of Asia-Pacific locations. Isotopic and elemental data (31 elements) were analysed using multivariate methods, linear discriminant analysis (LDA), and randomForest. LDA and randomForest had consistent results: XRF effectively distinguished the production method and geographic origin of P. monodon (up to 100% accuracy), while SIA had a lower accuracy (up to 95% accuracy). However, SIA and XRF are effective complementary methods for determining provenance of black tiger prawns. Crown Copyright © 2018 Published by Elsevier Ltd.
- 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, H; 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.
- ItemCritical thresholds in aquatic ecosystems: a case study of Tasmanian diatom community response to regional and local environmental change(Australian Society for Limnology, 2016-09-29) Beck, KK; Fletcher, MS; Saunders, KM; Benson, A; Gadd, PS; Heijnis, H; Wolfe, B; Zawadzki, AAquatic ecosystems are often hyper-sensitive and rapid responders to local and regional environmental change, in large part, due to fast reproduction and short lifespans of organisms relative to, for example, terrestrial vegetation. Here, we explore the response of a local diatom community to rapid shifts in rainforest vegetation driven by climate and fire over the last 2,400 years. We use a suite of palaeolimnological data to determine changes in vegetation, nutrient cycling, sediment delivery and diatom community structure to test the response of the local aquatic ecosystems to climate-driven terrestrial environment changes. We find that the diatom community in our study lake, Lake Vera in southwest Tasmania, Australia, remains complacent through phases of substantial changes in the terrestrial environment, hinting at a degree of resilience to both regional climatic and local terrestrial ecosystem change. We also identify a major compositional changes in diatom community – a shift from a planktonic dominance (i.e. Discostella stelligera) to a benthic dominance (i.e. Fragilaria spp. and Achnanthes didyma) – at ca. 930 cal yr BP, prior to a climate-driven terrestrial ecosystem change at ca. 800 cal yr BP. This aquatic ecosystem state-shift reflects the crossing of a critical threshold/tipping point in response to regional drivers and/or local dynamics that, thus, provides critical insights in to the long-term drivers and responses of aquatic ecosystem dynamics.
- 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, H; 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.
- ItemDeveloping tree-ring chronologies and climate reconstructions from moisture sensitive Araucariaceae trees in tropical and subtropical Australia(Australasian Quaternary Association Inc., 2018-12-10) Haines, HA; English, NB; Hua, Q; Olley, JM; Gadd, PS; Palmer, JG; Kemp, JMany parts of tropical and subtropical Australia lack both annually-resolved long-term instrumental climate data and proxy climate records. This limits our understanding of past climate patterns and impacts. There are however, remnant forest stands where dendroclimatology could be applied to extend the climate record. Tree species in these regions are known to be compromised by numerous ring anomalies and as such are understudied resulting in indistinct tree growth-climate relationships. Recent research of trees in the Araucariaceae family has attempted to address these issues with the goal being to develop long-term climate reconstructions across tropical and subtropical Australia. Araucariaceae trees are commonly found across northern and eastern Australia and are longer lived than many other local non-temperate species. They are known to produce growth rings that are mostly annual and their growth appears sensitive to climate, specifically to moisture conditions. Three Araucariaceae species, hoop pine (Araucaria cunninghamii), bunya pine (Araucaria bidwillii) and purple kauri pine (Agathis atropurpurea) have been studied at five locations within the rainforests of eastern Queensland. Ring anomalies including false, faint, locally absent, and pinching or wedging rings, were identified. This was done by applying bomb-pulse radiocarbon dating and Itrax radiographic analysis to hoop pine trees from subtropical Lamington and D’Aguilar National Parks respectively. Additionally, dendrometers were installed on trees of all three species so that the climate variables influencing seasonal growth could be identified. It was found that moisture conditions drive annual growth in Araucariaceae trees but that the onset and cessation of the growth season is dependent on temperature. Forest elevation also needs to be considered as the growth season length is longer at lower elevation and there is an influence of cloud cover seen in the north Queensland rainforest, which is close to a cloud forest classification. Annual growth was confirmed for all species through this analysis and the suitability for their use in climate reconstruction proven. Following this, a 164-year drought reconstruction for Southeast Queensland was developed using hoop pine trees from the subtropical rainforest of Lamington National Park. Additional work is continuing to further develop a network of long-term Queensland tree-ring climate records. © The Authors
- ItemDiscovery of a palaeolake at the terminus of the Murray-Darling Basin: a Holocene record of southeastern Australia’s hydroclimate and implications for current palaeoclimate reconstructions(International Union For Quaternary Research (INQUA), 2015-07-27) De Carli, E; Hubble, T; Penny, D; Petley, DN; Clarke, SL; Hamilton, RJ; Gadd, PS; Brand, HEAThe 1.073 million km2 Murray-Darling River Basin (MDB) drains 14% of Australia’s landmass, incorporates Australia’s most economically important agricultural region, and presents one of Australia’s most important and contentious water security challenges. In this study we report the discovery of a hitherto unrecognised terminal palaeolake system ’Lake Mannum’ that developed during the middle to late Holocene, as evidenced by an extensive sequence of laminated muds. The deposit contains grey coloured laminae rich in Fe and smectite, and olive-black coloured laminae K and illite rich, representing high discharge events from both the Darling and Murray River catchments respectively, providing a high-resolution proxy record of MDB hydroclimatic variability during the Holocene. Given the strong influence of major oceanic-atmospheric synoptic circulation features (ENSO, IOS-SAM, IPO, IDO) over the river system, variability in MDB discharge and delivery of suspended sediment flux to the continental shelf have been used as proxy indicators for southeastern Australian palaeoclimate during the Holocene. The existence of a lake system at the terminus of the MDB suggests that discharge of terrigenous sediment to the Southern Ocean was strongly suppressed during this time, meaning that Holocene climate reconstructions for SE Australia which rely on the marine sediment record require re-evaluation.
- ItemDust deposition tracks late-Holocene shifts in monsoon activity and the increasing role of human disturbance in the Puna-Altiplano, northwest Argentina(SAGE, 2020-04-01) Hooper, J; Marx, SK; May, JH; Lupo, LC; Kulemeyer, JJ; Pereira, EdlÁ; Seki, O; Heijnis, H; Child, DP; Gadd, PS; Zawadzki, AThe Puna-Altiplano plateau represents a regionally significant dust source, which is critically located at the nexus between the tropical and sub-polar synoptic systems that dominate the South American climate. Dust emissions in this region would therefore be expected to be sensitive to changes in these systems, in particular the strength and position of the South American Summer Monsoon (SASM). Here, we present a late-Holocene multi-proxy study where changes in dust flux, reconstructed from a high-altitude peat mire, are examined in light of climate variability and human impacts. Results show that for most the 4300 cal. yr BP record, dust flux sensitively tracked changes in SASM activity. Prior to 2600 cal. yr BP relatively high dust flux implies dry conditions prevailed across the Puna-Altiplao in association with reduced SASM activity. The chemistry of dust deposited at this time matched the large endorheic basins on the Puna, which host ephemeral lakes and terminal fans, indicating these were actively supplying dust to the airstream. After 2600 cal. yr BP, SASM activity increased while dust flux decreased and the dust chemistry changed, collectively implying the shutting down of the Puna-Altiplano as a significant dust source. Dust flux increased after 1000 cal. yr BP during the ‘Medieval Warm Period’, associated with a return to drier conditions and reactivation of dust sources across the endorheic basins of the Puna. Natural variability in dust flux was dwarfed, however, by the very significant increase in flux after 400 cal. yr BP following Spanish Colonisation and associated changing landuse practices. This finding attests to the globally significant role of humans on dust emissions. © 2020 by SAGE Publications