Browsing by Author "Grieg, A"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Last Glacial pluvial periods evident in subaqueous speleothems from Australia’s southern arid-margin
    (Australasian Quaternary Association Inc., 2022-12-06) Gould-Whaley, C; Drysdale, RN; May, JH; Hellstrom, JC; Treble, PC; Grieg, A; Cheng, H; Buswell, C
    Archives from Kati Thanda (Lake Eyre) basin indicate at least three distinct periods of lake filling during the Last Glacial Period. The headwaters of the megalake lie as far north as -19 °, therefore filling events are indicative of increased intensity of the Indo-Australian Summer Monsoon (IASM). However, due to the nature of unconsolidated materials, these archives are limited in how precisely they can constrain the timing of Last Glacial pluvial periods, and they cannot capture millennial-scale climate variability. Speleothems from Mairs Cave (Flinders Ranges, South Australia), present an opportunity to address these issues. The cave lies on the boundary between the arid and semi-arid regions and currently receives rainfall from both the Southern Hemisphere Westerly Winds (SHWW) and the IASM. The cave contains pendulites: stalactites with an external overgrowth of subaqueously precipitated calcite. The stalactites were initially submerged ~ 89 ka by rising groundwaters, which flooded the cave. From that point forward, the pendulites grew subaqueously during periods of regional groundwater recharge. Preliminary findings suggest periods of subaqueous growth align with higher Southern Hemisphere summer insolation, suggesting the site received enhanced tropical rainfall due to moisture delivery from the IASM. Growth rate and magnesium concentrations both appear to be responsive to millennial-scale climate change, exhibiting increases during both Heinrich events and the cold limbs of Dansgaard-Oeschger events. This is consistent with increased delivery of tropical moisture due to southerly incursions of the IASM. The study site lies near the intersection of two ‘superhighways’ of early human expansion proposed by Crabtree et al. (2021). The cave is also 200 km directly south of the Warratyi shelter, one of the earliest sites of human occupation in southern-central Australia. Therefore, the palaeoclimate record to emerge from this research could potentially provide a more detailed climatic contextualisation for this period of human history.
  • Thumbnail Image
    Item
    Magnesium in subaqueous speleothems as a potential palaeotemperature proxy
    (Springer Nature, 2020-10-06) Drysdale, RN; Couchoud, I; Zanchetta, G; Isola, I; Regattieri, E; Hellstrom, JC; Govin, A; Tzedakis, PC; Ireland, T; Corrick, E; Grieg, A; Wong, HKY; Piccini, L; Holden, PJ; Woodhead, JD
    Few palaeoclimate archives beyond the polar regions preserve continuous and datable palaeotemperature proxy time series over multiple glacial-interglacial cycles. This hampers efforts to develop a more coherent picture of global patterns of past temperatures. Here we show that Mg concentrations in a subaqueous speleothem from an Italian cave track regional sea-surface temperatures over the last 350,000 years. The Mg shows higher values during warm climate intervals and converse patterns during cold climate stages. In contrast to previous studies, this implicates temperature, not rainfall, as the principal driver of Mg variability. The depositional setting of the speleothem gives rise to Mg partition coefficients that are more temperature dependent than other calcites, enabling the effect of temperature change on Mg partitioning to greatly exceed the effects of changes in source-water Mg/Ca. Subaqueous speleothems from similar deep-cave environments should be capable of providing palaeotemperature information over multiple glacial-interglacial cycles. © 2020 The Author(s)