Reconstructing Australia’s late Quaternary climate from the geochemistry of lake sediments and snail shells

Australia’s climate is influenced by ocean-atmosphere interactions in the adjacent Indian, Pacific, and Southern oceans, as well as major atmospheric circulation patterns. Australian climates exhibit high inter-annual variability, arising in part from complex interactions between these drivers. Understanding the nature and drivers of Australian climate variability is not only important for land use and management, but also has global relevance, due to Australia’s contribution to the global terrestrial carbon budget. Measurements of Australian temperature and rainfall only extend back to the early 20th century, and hence do not capture the full range of natural climate variability. Proxy-based climate reconstructions are therefore required to understand Australian climate variability on long (centennial to millennial) time scales. The late Quaternary—defined in this thesis as 30 to 10 thousand years before the year 1950 (ka BP)—is a particularly informative interval. It encompasses large changes in global climate dynamics, including both the global Last Glacial Maximum (LGM; 23 to 19 ka BP) and subsequent deglaciation, allowing assessment of the Australian climate response to global change. However, the arid to semi-arid nature of most the continent is not conducive to sedimentary record accumulation, limiting spatial and temporal resolution of existing late Quaternary climate reconstructions. This thesis therefore presents both new late Quaternary palaeoclimate data and new methods for inferring past climate across the Australian continent, through the following research components: 1) A record of late Quaternary moisture balance, inferred from highly resolved x-ray fluorescence and organic carbon isotope measurements of a sedimentary sequence from Lake Surprise in south-eastern Australia (Chapter 3). The regional significance of this record is assessed using a Monte Carlo Empirical Orthogonal Function approach. 2) The high-resolution record is supported by three discrete quantitative temperature estimates, based on the clumped isotope composition (Δ47) of freshwater snail shells from Blanche Cave, also in south-eastern Australia (Chapter 6). Δ47 analysis allows calculation of the growth temperature of carbonate minerals (e.g. snail shells), independent of organism, carbonate phase, or formation water geochemistry. Carbonate Δ47 analysis therefore offers a uniquely direct estimate of past temperatures, that has not previously been applied in Australian palaeoclimate studies. 3) Clumped isotope analysis is highly susceptible to contamination, so this thesis provides a new pretreatment method for obtaining precise and accurate data from carbonates preserved within an organic-rich matrix (Chapter 2). 4) The influence of remote drivers of Australian climate often manifests in distinct spatial patterns of temperature or rainfall. However, the low spatial resolution of existing palaeoclimate records across the continent inhibits detection of spatio-temporal climate trends that would facilitate inference of these drivers. This thesis therefore evaluates the climate proxy potential of land snail shells in Australia, by combining flux balance models with clumped and stable isotope measurements of modern shells collected from a wide spatial and climatic gradient across the continent (Chapters 4 and 5). The palaeoclimate reconstructions provide a coherent record of climate variability prior to and throughout the late Quaternary, and suggest that drivers of south-eastern Australian climate have varied on multi-millennial time scales in response to major shifts in global circulation. Δ47 analysis of freshwater snail shells suggests that between ~41 and 32 ka BP, mean annual air temperatures at Blanche Cave decreased from approximately 12 ± 3.2 °C to 5 ± 4.4 °C i.e. almost ten degrees cooler than modern. These relatively low temperatures preceded a period of regional aridity between 28 and 18.5 ka BP as recorded at Lake Surprise. Together, the data suggest that the south-east Australian climate was probably responding to very different drivers to those that affect the modern climate, possibly dominated by cold Southern Ocean processes. Centennial- to millennial-scale hydroclimate variability was maintained throughout the 28–18.5 ka BP interval. Peak aridity between 21 and 18.5 ka BP probably represents the local expression of the global LGM. A rapid deglacial climate shift occurred between ~18.5 and 16 ka BP, culminating in warmer (15.5 ± 3.6 °C) and wetter conditions probably more like those of the present. The stable isotope geochemistry of modern land snail shells records precipitation amount via two mechanisms: (1) its influence on the δ18O of precipitation (a wet season signal), and (2) its effect on vegetation δ13C (an annual to multi-annual signal). Unlike freshwater snails, land snail Δ47 growth temperatures do not have a straightforward relationship with average air temperatures, but rather are useful for extracting the temperature influence from snail shell δ18O. This is the first study to report δ13C, δ18O, and Δ47 measurements from land snail shells spanning such a large climatic gradient, and also the first to investigate snail isotope-climate relationships across the variable and largely arid Australian environments. The isotope-climate relationships are robust irrespective of species or regional climatology. With land snails widely distributed in Australia, including in arid climates that lack other suitable proxies, these consistent relationships demonstrate that land snail shell isotopes will be a valuable tool for assessing spatio-temporal precipitation variability at a continental scale.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 201

The Iso2k Database: A global compilation of paleo-δ18O and δ2H records to aid understanding of Common Era climate

Reconstructions of global hydroclimate during the Common Era (CE; the past ~ 2000 years) are important for providing context for current and future global environmental change. Stable isotope ratios in water are quantitative indicators of hydroclimate on regional to global scales, and these signals are encoded in a wide range of natural geologic archives. Here we present the Iso2k database, a global compilation of previously published datasets from a variety of natural archives that record the stable oxygen (δ18O) or hydrogen (δ2H) isotopic composition of environmental waters, which reflect hydroclimate changes over the CE. The Iso2k database contains 756 isotope records from the terrestrial and marine realms, including: glacier and ground ice (205); speleothems (68); corals, sclerosponges, and mollusks (145); wood (81); lake sediments and other terrestrial sediments (e.g., loess) (158); and marine sediments (99). Individual datasets have temporal resolutions ranging from sub-annual to centennial, and include chronological data where available. A fundamental feature of the database is its comprehensive metadata, which will assist both experts and non-experts in the interpretation of each record and in data synthesis. Key metadata fields have standardized vocabularies to facilitate comparisons across diverse archives and with climate model simulated fields. This is the first global-scale collection of water isotope proxy records from multiple types of geological and biological archives. It is suitable for evaluating hydroclimate processes through time and space using large-scale synthesis, model-data intercomparison and (paleo)data assimilation. The Iso2k database is available for download at: https://doi.org/10.6084/m9.figshare.11553162 (McKay and Konecky, 2020)

The Iso2k database: a global compilation of paleo-δ18O and δ2H records to aid understanding of common era climate

Reconstructions of global hydroclimate during the Common Era (CE; the past ~2,000 years) are important for providing context for current and future global environmental change. Stable isotope ratios in water are quantitative indicators of hydroclimate on regional to global scales, and these signals are encoded in a wide range of natural geologic archives. Here we present the Iso2k database, a global compilation of previously published datasets from a variety of natural archives that record the stable oxygen (δ18O) or hydrogen (δ²H) isotopic composition of environmental waters, which reflect hydroclimate changes over the CE. The Iso2k database contains 756 isotope records from the terrestrial and marine realms, including: glacier and ground ice (205); speleothems (68); corals, sclerosponges, and mollusks (145); wood (81); lake sediments and other terrestrial sediments (e.g., loess) (158); and marine sediments (99). Individual datasets have temporal resolutions ranging from sub-annual to centennial, and include chronological data where available. A fundamental feature of the database is its comprehensive metadata, which will assist both experts and non-experts in the interpretation of each record and in data synthesis. Key metadata fields have standardized vocabularies to facilitate comparisons across diverse archives and with climate model simulated fields. This is the first global-scale collection of water isotope proxy records from multiple types of geological and biological archives. It is suitable for evaluating hydroclimate processes through time and space using large-scale synthesis, model-data intercomparison and (paleo)data assimilation. The Iso2k database is available for download at: https://doi.org/10.25921/57j8-vs18 (Konecky and McKay, 2020) and is also accessible via through the NOAA/WDS Paleo Data landing page: https://www.ncdc.noaa.gov/paleo/study/29593

Millennial-scale variability in south-east Australian hydroclimate between 30,000 and 10,000 years ago

Global climate variability during the late Quaternary is commonly investigated within the framework of the ‘bipolar seesaw’ pattern of asynchronous temperature variations in the northern and southern polar latitudes. 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. Elevated Si (reflecting windblown quartz and clays), and relatively high δ13COM, indicate an extended period of relative aridity between 28 and 18.5 ka BP, interrupted by millennial-scale episodes of decreased Si and δ13COM, suggesting increased moisture balance. This was followed by a rapid deglacial shift to low Si and δ13COM at 18.5 ka BP, indicative of wetter conditions. We find that these changes are coeval with other records from south-eastern Australia and New Zealand, and use a Monte Carlo Empirical Orthogonal Function approach to extract a common trend from three high-resolution records. 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 (around 18 ka BP), the southward migration of cold Southern Ocean fronts likely resulted in the establishment of conditions more like those of the present day. Millennial-scale variability in records from the region is dominated by a persistent ca. 2300-year periodicity, consistent with other records across the Southern Hemisphere mid-latitudes; however, this pervasive periodicity is not obviously linked to the ‘bipolar seesaw’ and the mechanism remains equivocal.This research was partially funded by an ARC Discovery Project (grant number DP140014093). The authors would like to thank AINSE Limited for providing a Postgraduate Research Award to G. Falster to enable acquisition of new radiocarbon dates (grant number ALNSTU11873). G. Falster received support for this research through the provision of an Australian Government Research Training Program Scholarship. The authors also acknowledge the financial support from the Australian Government for the Centre for Accelerator Science at ANSTO through the National Collaborative Research Infrastructure Strategy

Gestational Age and Child Development at Age Five in a Population-Based Cohort of Australian Aboriginal and Non-Aboriginal Children

Background: Preterm birth and developmental vulnerability are more common in Australian Aboriginal compared with non-Aboriginal children. We quantified how gestational age relates to developmental vulnerability in both populations. Methods: Perinatal datasets were linked to the Australian Early Development Census (AEDC), which collects data on five domains, including physical, social, emotional, language/cognitive, and general knowledge/communication development. We quantified the risk of developmental vulnerability on ≥1 domains at age 5, according to gestational age and Aboriginality, for 97 989 children born in New South Wales, Australia, who started school in 2009 or 2012. Results: Seven thousand and seventy-nine children (7%) were Aboriginal. Compared with non-Aboriginal children, Aboriginal children were more likely to be preterm (5% vs. 9%), and developmentally vulnerable on ≥1 domains (20% vs. 36%). Overall, the proportion of developmentally vulnerable children decreased with increasing gestational age, from 44% at ≤27 weeks to 20% at 40 weeks. Aboriginal children had higher risks than non-Aboriginal children across the gestational age range, peaking among early term children (risk difference [RD] 19.0, 95% confidence interval [CI] 16.3, 21.7; relative risk [RR] 1.91, 95% CI 1.77, 2.06). The relation of gestational age to developmental outcomes was the same in Aboriginal and non-Aboriginal children, and adjustment for socioeconomic disadvantage attenuated the risk differences and risk ratios across the gestational age range. Conclusions: Although the relation of gestational age to developmental vulnerability was similar in Aboriginal and non-Aboriginal children, Aboriginal children had a higher risk of developmental vulnerability at all gestational ages, which was largely accounted for by socio-economic disadvantage

The absolute risk of developmental vulnerability on the language and cognitive skills and communication skills and general knowledge domains of the AEDC, and vulnerability on ≥1 AEDC domains, for every year of maternal age at childbirth between 15 and 45 years.

<p>Model 1 includes adjustment for the child’s age at school entry, sex, and AEDC year; in addition to the covariates included in Model 1, Model 2 adjusts for private health insurance/patient status, mother born in Australia/overseas, mother partnered/single parent, mother’s parity, child’s Aboriginality, whether child speaks English as a second language, highest level of maternal school education, highest level of occupation of either parent, area-level disadvantage, and geographical remoteness; in addition to the covariates included in Model 2, Model 3 adjusts for antenatal care visit before 20 weeks gestation, smoking during pregnancy, and preschool/day care attendance in the year before school. AEDC, Australian Early Development Census.</p

Coefficients for 1-year increase in maternal age between 15–<30 years, and ≥35–45 years, from piecewise linear regression models.

<p>Coefficients for 1-year increase in maternal age between 15–<30 years, and ≥35–45 years, from piecewise linear regression models.</p

The distribution of maternal age at childbirth for children in the study population, overlaid with the proportion of children who were developmentally vulnerable on each outcome, by maternal age at childbirth.

<p>Light grey columns, study population birth distribution by year of maternal age at childbirth; black point estimates with 95% CIs, proportion of children developmentally vulnerable on each outcome (specified in figure subtitle).</p

The absolute risk of developmental vulnerability on the physical health and well-being, social competence, and emotional maturity domains of the AEDC for every year of maternal age at childbirth between 15 and 45 years.

<p>Model 1 includes adjustment for the child’s age at school entry, sex, and AEDC year; in addition to the covariates included in Model 1, Model 2 adjusts for private health insurance/patient status, mother born in Australia/overseas, mother partnered/single parent, mother’s parity, child’s Aboriginality, whether child speaks English as a second language, highest level of maternal school education, highest level of occupation of either parent, area-level disadvantage, and geographical remoteness; in addition to the covariates included in Model 2, Model 3 adjusts for antenatal care visit before 20 weeks gestation, smoking during pregnancy, and preschool/day care attendance in the year before school. AEDC, Australian Early Development Census.</p

Sociodemographic, pregnancy, and early childhood characteristics, by maternal age at childbirth, for the 99,530 children in the study population¹.

<p>Sociodemographic, pregnancy, and early childhood characteristics, by maternal age at childbirth, for the 99,530 children in the study population<a href="http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.1002558#t001fn001" target="_blank">¹</a>.</p