Browsing by Author "Abram, NJ"

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    Caves demonstrate decrease in rainfall recharge of southwest Australian groundwater is unprecedented for the last 800 years
    (Springer Nature, 2023-06-09) Priestley, SC; Treble, PC; Griffiths, AD; Baker, AA; Abram, NJ; Meredith, KT
    Billions of people worldwide rely on groundwater. As rainfall in many regions in the future is projected to decrease, it is critical to understand the impacts of climate change on groundwater recharge. The groundwater recharge response to a sustained decrease in rainfall across southwest Australia that began in the late 1960s was examined in seven modern speleothems and drip waters from four caves. These show a pronounced increase or uptick in regional drip water and speleothem oxygen isotopic composition (δ18O) that is not driven by a change in rainfall δ18O values, but is in response to the shallow karst aquifers becoming disconnected from rainfall recharge due to regional drying. Our findings imply that rainfall recharge to groundwater may no longer be reliably occurring in this region, which is highly dependent on groundwater resources. Examination of the longer speleothem record shows that this situation is unprecedented over the last 800 years. © The Authors - Open Access licensed under a Creative Commons Attribution 4.0 International Licence.
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    Caves provide early warning of unprecedented decrease in rainfall recharge of groundwater
    (Research Square, 2022-05-02) Priestley, SC; Treble, PC; Griffiths, AD; Baker, AA; Abram, NJ; Meredith, KT
    Billions of people worldwide rely on groundwater. As rainfall in many regions in the future is projected to decrease, it is critical to understand the impacts of climate change on groundwater recharge. In this study, five caves record a consistent response to a sustained decrease in rainfall across southwest Australia that began in the late 1960s, characterised by a pronounced increase or ’uptick’ in dripwater and speleothem oxygen isotopic composition (δ18O). It is demonstrated that the uptick is in response to the shallow karst aquifers becoming disconnected from recharge due to regional drying. Our findings imply that rainfall recharge to groundwater across this region is no longer reliably occurring. Examination of the longer speleothem record shows that this is unprecedented over at least the last 800 years. A global network of cave dripwater monitoring would serve as an early warning of reduced groundwater recharge elsewhere, while evidence for upticks in speleothem paleoclimate records would provide a longer-term context to evaluate if current groundwater recharge changes are outside the range of natural variability. This study also validates speleothems as recorders of past hydroclimate via amplification of the δ18O signal by karst hydrology highlighting that speleothem δ18O are records of recharge, rather than a direct proxy for rainfall. © 2022 The Authors
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    The CoralHydro2k Database: a global compilation of coral δ18O and Sr/Ca records for reconstructing tropical hydroclimate over the common era
    (American Geophysical Union (AGU), 2021-12-18) Sayani, HR; Walter, R; Felis, T; Cobb, KM; Abram, NJ; Atwood, AR; Arzey, A; Brenner, LD; Dassie, EP; DeLong, KL; Ellis, B; Goodkin, N; Hargreaves, J; Kilbourne, KH; Krawczyk, H; Fischer, MJ; Murty, SA; Moore, AL; Ramos, RDP; Reed, E; Samanta, D; Zinke, J
    Shallow-water corals provide annual to subannual -resolution climate reconstructions from normally data-scarce locations in the tropical to subtropical oceans, enabling us to extend the modern-day observational records back to the preindustrial era, contextualize anthropogenic climate change, and improve the skill of future climate projections. The majority of these coral-based reconstructions utilize oxygen isotope ratios (δ18O), a proxy that tracks the combined change in sea surface temperature (SST) and the oxygen isotopic composition of seawater (δ18Osw) and/or strontium-to-calcium ratios (Sr/Ca), which primarily track SST variability. Paired coral δ18O and Sr/Ca records can be combined to isolate δ18Osw variability, which like salinity reflects changes in the local hydrologic budget. Recently, the PAGES Ocean2k project used published coral records to reconstruct regional SST variability across the tropical oceans (Tierney et al., 2015, Abram et al., 2016). Building on this work, the PAGES CoralHydro2k team has compiled a more comprehensive, machine-readable, and metadata-rich network of paired coral δ18O and Sr/Ca records to help facilitate tropical hydroclimate reconstructions across recent centuries. The CoralHydro2k database currently contains 227 coral proxy records from 120 unique locations that are organized into seven tiers based on the availability of paired proxy data, temporal coverage, and record resolution. The metadata for the new database follows PACTs 1.0 recommendations (Khider et al., 2019), and the database is built using LiPD (McKay and Emile-Geay, 2016) with available R, MATLAB, and Python serializations. Here we describe the structure and spatiotemporal characteristics of this new database and outline a crowdsourced data-submission process to ensure active-curation of records and future updates to the database.
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    Past hydroclimatic variability from southwest Australian speleothems during the last millennium
    (Australiasian Quaternary Association Inc., 2018-12-10) Treble, PC; Baker, AA; Griffiths, AD; Hellstrom, JC; Bajo, P; Abram, NJ; Fairchild, IJ; Borsato, A; Markowska, M; Gagan, MK
    Speleothems from Golgotha Cave in SW Western Australia have been investigated to extend our knowledge of past climate variability for this region during the last millennium. O isotopic datasets, the primary paleoclimate proxy used for speleothems, were constructed for four stalagmites. A challenge in their interpretation has been the disagreement between these records, despite representing coeval growth from within the same cave. Resolving this conundrum has necessitated the characterisation of the hydrology, hydrochemistry, rainfall isotopes7 and development of proxy system forward models1,8 for Golgotha Cave. The findings of these studies will be summarised as a conceptual model in order to present the main karst hydrological features that give rise to each stalagmite’s isotopic response to hydroclimatic forcing. The paleoclimate interpretation will focus on the two continuous stalagmite records that were fed predominately by diffuse flow. This will be supported by evidence from the two stalagmites predominantly fed by fracture flow, which has resulted in a non-linear response to hydroclimatic forcing.
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    Speleothem ‘uptick’ supports reduction in rainfall recharge to groundwater is unprecedented for last 800 years, SW Western Australia
    (Australasian Quaternary Association, 2022-12-06) Priestley, SC; Treble, PC; Baker, AA; Griffiths, AD; Abram, NJ; Meredith, KT
    Southwestern Australia relies significantly on groundwater for domestic and industrial purposes. As water availability has decreased and is projected to continue to decrease with climate change, it is critical to understand the impacts of climate change on groundwater recharge for this region. Speleothem (e.g. cave stalagmites) deposition is directly related to groundwater recharge, as they form from rainfall which has infiltrated into the vadose zone and represent periods of potential aquifer recharge. In this study, modern speleothems from five caves record a consistent response to a sustained decrease in rainfall across south-west Australia that began in the 1970s, characterised by an ‘uptick’ in the speleothem oxygen isotopic composition (Priestley et al., 2022). It is demonstrated that the ‘uptick’ is in response to the shallow karst aquifers becoming disconnected from rainfall recharge due to regional drying. As the coastal caves are located in highly permeable host rock along the wettest zone of the region, our findings imply that rainfall recharge to groundwater across the southwest Australian region may no longer be reliably occurring. The paleo-record for speleothems from south-west Australia (Treble et al., 2022) provides a longer-term context to assess the recent isotopic uptick against and confirms that no similar events are seen in the last 800 years in stalagmites from the region.
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    Ubiquitous karst hydrological control on speleothem oxygen isotope variability in a global study
    (Springer Nature, 2022-02-15) Treble, PC; Baker, AA; Abram, NJ; Hellstrom, JC; Crawford, J; Gagan, MK; Borsato, A; Griffiths, AD; Bajo, P; Markowska, M; Priestley, SC; Hankin, SI; Paterson, DJ
    Speleothem oxygen isotopic (δ18O) records are used to reconstruct past hydroclimate yet records from the same cave do not always replicate. We use a global database of speleothem δ18O to quantify the replicability of records to show that disagreement is common worldwide, occurs across timescales and is unrelated to climate, depth or lithology. Our global analysis demonstrates that within-cave differences in mean speleothem δ18O values are consistent with those of dripwater, supporting a ubiquitous influence of flowpaths. We present a case study of four new stalagmite records from Golgotha Cave, southwest Australia, where the isotopic differences between them are informed by cave monitoring. It is demonstrated that karst hydrology is a major driver of within-cave speleothem and dripwater δ18O variability, primarily due to the influence of fractures on flowpaths. Applying our understanding of water movement through fractures assists in quantitative reconstruction of past climate variability from speleothem δ18O records. © The Authors - Open Access under a Creative Commons Attribution 4.0 International License.
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    Ubiquitous karst hydrological control on speleothem oxygen isotope variability in a global study
    (Springer Nature, 2022-02-15) Treble, PC; Baker, AA; Abram, NJ; Hellstrom, JC; Crawford, J; Gagan, MK; Borsato, A; Griffiths, AD; Bajo, P; Markowska, M; Priestley, SC; Hankin, SI; Paterson, DJ
    Speleothem oxygen isotopic (δ18O) records are used to reconstruct past hydroclimate yet records from the same cave do not always replicate. We use a global database of speleothem δ18O to quantify the replicability of records to show that disagreement is common worldwide, occurs across timescales and is unrelated to climate, depth or lithology. Our global analysis demonstrates that within-cave differences in mean speleothem δ18O values are consistent with those of dripwater, supporting a ubiquitous influence of flowpaths. We present a case study of four new stalagmite records from Golgotha Cave, southwest Australia, where the isotopic differences between them are informed by cave monitoring. It is demonstrated that karst hydrology is a major driver of within-cave speleothem and dripwater δ18O variability, primarily due to the influence of fractures on flowpaths. Applying our understanding of water movement through fractures assists in quantitative reconstruction of past climate variability from speleothem δ18O records. © Crown 2022 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.