Anthony Stuart Kiem

The Southern Annular Mode (SAM) represents the dominant pattern of climate variability in the extratropical Southern Hemisphere. However, its signature in coastal East Antarctic ice core records is unclear. A daily synoptic typing data set for the southern Indian Ocean constructed using self‐organizing maps on 500 hPa daily geopotential height anomalies was used to investigate the relationship between the SAM and ice core records from Law Dome and Mount Brown South. Results indicate that synoptic weather regimes can either enhance or suppress the signature of the SAM on surface weather and ice core records. Weather regimes that are more likely during negative SAM and are associated with positive temperature anomalies over East Antarctica support the observed relationship between the SAM and the Law Dome δ ¹⁸ O record since 1979. In contrast, weather regimes that describe meridional moisture flux toward Antarctica explain more snowfall accumulation variability at the ice core sites compared to the SAM, which contributes to suppressing the SAM signal in snowfall accumulation records. Results highlight the importance of considering the synoptic‐scale dynamics on the relationship and stationarity of the SAM influence on surface weather and interpretation of ice core records. Given the limited robust relationships between the SAM and the ice core records investigated, caution should be taken before using these records to reconstruct past SAM variability. Instead, the coastal East Antarctic ice core records provide insight into the occurrence of meridional weather regimes, which are often associated with extreme temperature and precipitation conditions.

Understanding past climate is essential to our knowledge of how our current climate system operates, and how it might respond to future change. Techniques to reconstruct climate history are challenging, and both accuracy and certainty are hampered by the quality of the datasets used. Here we both develop a new reconstruction tool and apply it to four ice core proxy based multi-millennial Holocene climate reconstructions, chosen because of their potential influence on East Antarctic climate. The new multi-proxy reconstruction method is called Segmented Linear Integral Correlation Kernel Ensemble Reconstruction (SLICKER). This method employs a segmented linear rather than Gaussian correlation approach and builds an ensemble of reconstructions with a best fit and spread related to the best estimate of uncertainty. This method is robust for non-linear, uneven or differently sampled data and produces high-fidelity reconstructions and associated uncertainty estimates. This new method has the potential to produce more realistic reconstructions, with associated uncertainty estimates based on robust statistical measures that are insensitive to outliers. The main findings from these new reconstructions are: Antarctica temperature shows multi-decadal variability over the last twelve thousand years with increased frequency over the last two thousand years; Zonal Wave 3 index and the Southern Annular Mode both show limited trends over the last two thousand years, but an increase since the 1970s CE; and the Indian Ocean Dipole Moment index has a twentieth century CE upward trend, and a thirteenth to sixteenth century CE below average period which may be related to volcanic activity.

Australia’s record-breaking 2019/20 Black Summer fire weather resulted from a combination of natural and anthropogenic climate factors, but the full range of natural variability in fire weather is unknown. We reconstruct southeast Australian fire weather over the Common Era based on an East Antarctic ice core sea-salt aerosol record. This record reflects the Southern Ocean synoptic-scale weather patterns and Antarctic stratospheric polar vortex strength that pre-condition elevated fire danger over southeast Australia. We show that the (a) intensity of the 2019/20 fire weather was unprecedented since 1950 and (b) frequency of above average fire weather seasons from 2010–2020 has only occurred once since 1950 (over 1977–1987), but there are analogues for similar extreme fire danger caused by natural variability in the 2000-year reconstruction. This highlights the need for fire risk mitigation that considers the full range of plausible natural variability in Australia’s fire weather as well as anthropogenic forcing.

Mineral prospectivity mapping is a crucial technique for discovering new economic mineral deposits. However, detailed knowledge-based geological exploration and interpretations generally involve significant costs, time, and human resources. In this study, an ensemble machine learning approach was tested using geoscience datasets to map Cu-Au and Pb-Zn mineral prospectivity in the Cobar Basin, NSW, Australia. The input datasets (magnetic, gravity, faults, electromagnetic, and magnetotelluric data layers) were chosen by considering their association with Cu-Au and Pb-Zn mineralization patterns. Three machine learning algorithms, namely random forest (RF), support vector machine (SVM), and maximum-likelihood (MaxL) classification, were applied to the input data. The results of the three algorithms were ensembled to produce Cu-Au and Pb-Zn prospectivity maps over the Cobar Basin with improved classification accuracy. The findings demonstrate good agreement with known mineral occurrence points and existing mineral prospectivity maps developed using the weights-of-evidence (WofE) method. The ability to capture training points accurately and the simplicity of the proposed approach make it advantageous over complex mineral prospectivity mapping methods, to serve as a preliminary evaluation technique. The methodology can be modified with different datasets and algorithms, facilitating the investigations of mineral prospectivity in other regions and providing guidance for more detailed, high-resolution geological investigations.

The Millennium Drought lasted more than a decade and is notable for causing persistent shifts in the relationship between rainfall and runoff in many southeastern Australian catchments. Research to date has successfully characterised where and when shifts occurred and explored relationships with potential drivers, but a convincing physical explanation for observed changes in catchment behaviour is still lacking. Originating from a large multi-disciplinary workshop, this paper presents and evaluates a range of hypothesised process explanations of flow response to the Millennium Drought. The hypotheses consider climatic forcing, vegetation, soil moisture dynamics, groundwater, and anthropogenic influence. The hypotheses are assessed against evidence both temporally (e.g. why was the Millennium Drought different to previous droughts?) and spatially (e.g. why did rainfall–runoff relationships shift in some catchments but not in others?). Thus, the strength of this work is a large-scale assessment of hydrologic changes and potential drivers. Of 24 hypotheses, 3 are considered plausible, 10 are considered inconsistent with evidence, and 11 are in a category in between, whereby they are plausible yet with reservations (e.g. applicable in some catchments but not others). The results point to the unprecedented length of the drought as the primary climatic driver, paired with interrelated groundwater processes, including declines in groundwater storage, altered recharge associated with vadose zone expansion, and reduced connection between subsurface and surface water processes. Other causes include increased evaporative demand and harvesting of runoff by small private dams. Finally, we discuss the need for long-term field monitoring, particularly targeting internal catchment processes and subsurface dynamics. We recommend continued investment in the understanding of hydrological shifts, particularly given their relevance to water planning under climate variability and change.

Previous research has shown that aerosol sea salt concentrations (Southern Ocean wind proxy) preserved in the Law Dome ice core (East Antarctica) correlate significantly with subtropical eastern Australian rainfall. However, physical mechanisms underpinning this connection have not been established. Here we use synoptic typing to show that an atmospheric bridge links East Antarctica to subtropical eastern Australia. Increased ice core sea salt concentrations and wetter conditions in eastern Australia are associated with a regional, asymmetric contraction of the mid-latitude westerlies. Decreased ice core sea salt concentrations and drier eastern Australia conditions are associated with an equatorward shift in the mid-latitude westerlies, suggesting greater broad-scale control of eastern Australia climate by southern hemisphere variability than previously assumed. This relationship explains double the rainfall variance compared to El Niño-Southern Oscillation during late spring-summer, highlighting the importance of the Law Dome ice core record as a 2000-year proxy of eastern Australia rainfall variability.

The Millennium Drought lasted more than a decade, and is notable for causing persistent shifts in the relationship between rainfall and runoff in many south-east Australian catchments. Research to date has successfully characterised where and when shifts occurred and explored relationships with potential drivers, but a convincing physical explanation for observed changes in catchment behaviour is still lacking. Originating from a large multi-disciplinary workshop, this paper presents a range of possible process explanations of flow response, and then evaluates these hypotheses against available evidence. The hypotheses consider climatic forcing, vegetation, soil moisture dynamics, groundwater, and anthropogenic influence. The hypotheses are assessed against evidence both temporally (eg. why was the Millennium Drought different to previous droughts?) and spatially (eg. why did rainfall-runoff relationships shift in some catchments but not in others?). The results point to the unprecedented length of the drought as the primary climatic driver, paired with interrelated groundwater processes, including: declines in groundwater storage, reduced recharge associated with vadose zone expansion, and reduced connection between subsurface and surface water processes. Other causes include increased evaporative demand and interception of runoff by small private dams. Finally, we discuss the need for long-term field monitoring, particularly targeting internal catchment processes and subsurface dynamics. We recommend continued investment in understanding of hydrological shifts, particularly given their relevance to water planning under climate variability and change.

The Interdecadal Pacific Oscillation, an index which defines decadal climate variability throughout the Pacific, is generally assumed to have positive and negative phases that each last 20-30 years. Here we present a 2000-year reconstruction of the Interdecadal Pacific Oscillation, obtained using information preserved in Antarctic ice cores, that shows negative phases are short (7 ± 5 years) and infrequent (occurring 10% of the time) departures from a predominantly neutral-positive state that lasts decades (61 ± 56 years). These findings suggest that Pacific Basin climate risk is poorly characterised due to over-representation of negative phases in post-1900 observations. We demonstrate the implications of this for eastern Australia, where drought risk is elevated during neutral-positive phases, and highlight the need for a re-evaluation of climate risk for all locations affected by the Interdecadal Pacific Oscillation. The initiation and future frequency of negative phases should also be a research priority given their prevalence in more recent centuries.