Browsing by Author "Leng, MJ"

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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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    Evaluating δ18O and δ13C variations within a modern Biggenden Banded snail (Figuladra bayensis) shell using radiocarbon dating: application for past climate reconstruction
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Patton, NR; Shulmeister, J; Leng, MJ; Jones, M; Hua, Q; Hughes, CE
    Gastropods are utilized to infer paleoclimate variability due to the preservation and incorporation of stable isotopes (δ18O and δ13C) in their aragonite shells. Analyses along the growth axis of larger gastropods have been suggested to contain high-resolution records of local seasonal climate variability and the organism’s biological life cycle. Here a Figuladra bayensis (Biggenden Banded snail) shell was collected shortly after death from Coalstoun Lakes National Park, Queensland, Australia. A total of 200 samples were collected for δ18O and δ13C analyses and an additional 8 radiocarbon dating samples were collected along the growth axis from the apex to the aperture. Results from our work indicates that the Biggenden Banded snail lived ~4.4 years, with evidence of two aestivation (dormant stage) periods during the dry, cool winters. As a result, its growth rate was episodic with the highest rates of ~90 mm/yr occurring shortly after large rain events. The δ18O and δ13C variation in the shell is closely related to total rainfall, diet and physiological changes. To our knowledge this is the highest resolution isotopic and radiocarbon dated study on a modern terrestrial snail, allowing the nuances of the stable isotope record to be more clearly interpreted and therefore used as a palaeoenvironmental proxy. © 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
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    Holocene sediment records from World Heritage-listed K'gari/Fraser Island lakes (subtropical eastern Australia) highlight their sensitivity to drying
    (International Union for Quaternary Research (INQUA), 2019-07-30) Tibby, J; Barr, C; McInerney, F; Murphy, C; Raven, M; Leng, MJ; Tyler, JJ; Marshall, JC; McGregor, GB; Gadd, PS
    Lakes are some of the most biodiverse, yet vulnerable, ecosystems on the planet. In Australia, the driest inhabited continent on earth, permanent lakes are relatively rare. By contrast, K'gari or Fraser Island, the largest sand island in the world, has a large number of permanent lakes and represents one of the few lake districts on the continent. The lakes of K'gari/Fraser island are remarkable because many are perched above the regional water table where an impermeable layer separates them from the sand below. They are one of the reasons why the island is listed as a UNESCO World Heritage site. Holocene sediment sequences have now been analysed from at least six lakes on K'gari/Fraser Island. It appears that there was marked aridity on the island from c. 8000 to 5000 ka BP. Some lakes dried completely at a time previously thought to be characterised by humid climates in the Australian subtropics. Interestingly, in some sequences there is little to no physical evidence of drying which is recorded as a hiatus in the accumulation of highly organic, acidic, lake sediments. The mid-Holocene dry phase recorded on K'gari/Fraser Island contrasts with evidence from North Stradbroke Island, a similar sand island which also has perched lakes, approximately 150 km to the south. As a result, there is strong potential to infer the Holocene regional climatology of the Australian subtropics at small spatial scales from these records. Lastly, our study highlights a largely unrecognised vulnerability of lakes on K’gari to drying and indicates a need to better understand their hydrology and response to projected future climate change. © The Authors.