Browsing by Author "Schulz, C"

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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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    A Holocene subtropical hydroclimate reconstruction from Karboora (Blue Lake), Minjerribah, Queensland
    (Australasian Quaternary Association, 2022-12-06) Maxson, C; Tibby, J; Tyler, JJ; Marshall, J; McGregor, G; Schulz, C; Jacobsen, GE; Klaebe, RM
    Holocene palaeoclimatology provides insights into the climate system, with particular relevance to the next century. This is especially true in sub-tropical Australia due to the under representation of the region in Holocene climate studies. Karboora (Blue Lake), on Minjerribah (North Stradbroke Island), Queensland, Australia is a groundwater window lake of major ecological and cultural significance. The lake’s strong connection with the regional aquifer underpins lake level stability, rendering Blue Lake sediments an ideal tracer of subtle changes in climate. Here, we report a new 5,500-year oxygen isotope record from biogenic (diatom) silica (δ18OBSi) that records variations in rainfall resulting from changes in Pacific atmospheric circulation. These interpretations are supported by modern monitoring over a 20 month period, including the δ18O of lake water, rain water, plant cellulose, and biogenic silica. We link rain δ18O to changes in El Niño Southern Oscillation (ENSO) phases, with phases showing distinct isotopic change that may be linked to tropical or extratropical sources of rainfall. On these grounds, we infer a dominance of extratropical rainfall from 5.5 kyr BP to 3.5 kyr BP, a period of transition from 3.5 kyr BP to 2.5 kyr BP dominated by neither tropical or extratropical rainfall, then a shift to tropically sourced rain from 2.5 kyr BP to the present. The early record (5.5 kyr BP – 3.5 kyr BP) most likely reflects a suppression of summer rainfall caused by a weakened ENSO. This is most likely linked to higher northern hemisphere insolation causing a northward shift in the intertropical convergence zone and westerly wind belt which in turn affected synoptic systems in the Coral and Tasman Seas. The increasing variability in the late record (3.5 kyr BP to present) most likely represents an increase in summer rainfall driven by the intensification of ENSO in the late Holocene.
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    A Holocene subtropical hydroclimate reconstruction from Karboora (Blue Lake), Minjerribah, Queensland
    (Australasian Quaternary Association Inc., 2022-12-06) Maxson, C; Tibby, J; Tyler, JJ; Marshall, JC; McGregor, G; Schulz, C; Jacobsen, GE; Klaebe, R
    Holocene palaeoclimatology provides insights into the climate system, with particular relevance to the next century. This is especially true in sub-tropical Australia due to the under representation of the region in Holocene climate studies. Karboora (Blue Lake), on Minjerribah (North Stradbroke Island), Queensland, Australia is a groundwater window lake of major ecological and cultural significance. The lake’s strong connection with the regional aquifer underpins lake level stability, rendering Blue Lake sediments an ideal tracer of subtle changes in climate. Here, we report a new 5,500-year oxygen isotope record from biogenic (diatom) silica (δ18OBSi) that records variations in rainfall resulting from changes in Pacific atmospheric circulation. These interpretations are supported by modern monitoring over a 20 month period, including the δ18O of lake water, rain water, plant cellulose, and biogenic silica. We link rain δ18O to changes in El Niño Southern Oscillation (ENSO) phases, with phases showing distinct isotopic change that may be linked to tropical or extratropical sources of rainfall. On these grounds, we infer a dominance of extratropical rainfall from 5.5 kyr BP to 3.5 kyr BP, a period of transition from 3.5 kyr BP to 2.5 kyr BP dominated by neither tropical or extratropical rainfall, then a shift to tropically sourced rain from 2.5 kyr BP to the present. The early record (5.5 kyr BP – 3.5 kyr BP) most likely reflects a suppression of summer rainfall caused by a weakened ENSO. This is most likely linked to higher northern hemisphere insolation causing a northward shift in the intertropical convergence zone and westerly wind belt which in turn affected synoptic systems in the Coral and Tasman Seas. The increasing variability in the late record (3.5 kyr BP to present) most likely represents an increase in summer rainfall driven by the intensification of ENSO in the late Holocene.
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    Reading the tea-tree leaves: Melaleuca quinquenervia leaves as a palaeoclimate proxy
    (International Union for Quaternary Research (INQUA), 2019-07-30) Geer, J; McInerney, F; Tibby, J; Hua, Q; Schulz, C; Barr, C; Marshall, J; McGregor, G
    The analysis of organic material preserved in sedimentary records is a useful tool in reconstructing past climatic conditions. It has been suggested that the carbon isotope discrimination (Δ) calculated from the bulk leaf δ13C of the modern Melaleuca quinquenervia tree responds to local precipitation in south-east Queensland, Australia [1]. The preservation of these leaves in lake sediments on Minjerribah (North Stradbroke Island) dating to the mid-Holocene presents the opportunity to produce species-specific stable isotope-based records of precipitation. Here, we test the potential for M. quinquenervia to be used as a palaeoclimate proxy by examining the preservation of the bulk leaf δ13C over time and the relationship of Δ values to historical records of precipitation. Due to the varying rates of degradation of the different chemical constituents of plant matter, it is possible δ13C ratios to be altered by early diagenetic processes before, or during, the incorporation of leaves into the sediment. Therefore, modern studies are needed to establish what factors influence the discrimination derived precipitation record. Focusing on the M. quinquenervia growing at Swallow Lagoon on Minjerribah, we studied the changes to the bulk leaf δ13C ratios of exposed leaves over an eighteen-month field study. We then applied our findings to the measured δ13C ratios of bulk leaf material retrieved from a core taken from the lagoon. The Δ values calculated based on these measurements were then compared to instrumental rainfall data from the past century to test the established relationship with modern precipitation through time. By bisecting each leaf used in this study, we were able to compare the experimentally degraded leaves directly to their corresponding control halves. We observed that decay causes an approximate decrease of 1 ‰ in δ13C, as the leaves become more 13C depleted relative to the control leaf halves that were dried immediately. Quantifying this offset enables adjustment of values to be comparable to the calibration equation established using natural fall leaves from modern M. quinquenervia. Comparing the adjusted Δ values for lake core leaves from the last century to corresponding rainfall data the relationship to local precipitation seems to be preserved. Understanding exactly how early diagenesis changes the stable isotope composition of M. quinquenervia leaf material over time allows us to adjust for the offset between modern and sub-fossil bulk leaf δ13C and advances the potential to use this species as a reliable climate proxy in the future. © The authors.