School of Earth Sciences - Research Publications

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Author: Couchoud, Isabelle × Author: Hellstrom, John × End date: 2023 × Start date: 2020 × Type: Journal Article ×

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    Magnesium in subaqueous speleothems as a potential palaeotemperature proxy
    Drysdale, R ; Couchoud, I ; Zanchetta, G ; Isola, I ; Regattieri, E ; Hellstrom, J ; Govin, A ; Tzedakis, PC ; Ireland, T ; Corrick, E ; Greig, A ; Wong, H ; Piccini, L ; Holden, P ; Woodhead, J (NATURE RESEARCH, 2020-10-06)
    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.
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    Speleothem growth intervals reflect New Zealand montane vegetation response to temperature change over the last glacial cycle.
    Hellstrom, J ; Sniderman, K ; Drysdale, R ; Couchoud, I ; Hartland, A ; Pearson, A ; Bajo, P (Springer Nature, 2020-02-12)
    Flowstone speleothem growth beneath Mount Arthur, New Zealand shows a clear relationship to vegetation density and soil development on the surface above. Flowstone does not currently form beneath sub-alpine Nothofagus forest above ca. 1000-1100 m altitude but U-Th dating shows it has formed there during past intervals of warmer-than-present conditions including an early-mid Holocene optimum and the last interglacial from ca. 131-119 ka. Some flowstones growing beneath ca. 600 m surface altitude, currently mantled with dense broadleaf-podocarp forest, grew during full glacial conditions, indicating that local tree line was never below this altitude. This implies that Last Glacial Maximum annual temperature was no more than ca. 4 °C cooler than today. Flowstone growth appears to be a robust indicator of dense surface vegetation and well-developed soil cover in this setting, and indicates that past interglacial climates of MIS 7e, 5e, the early-mid Holocene and possibly MIS 5a were more conducive to growth of trees than was the late Holocene, reflecting regional temperature changes similar in timing to Antarctic temperature changes. Here, flowstone speleothem growth is a sensitive indicator of vegetation density at high altitude, but may respond to other factors at lower altitudes.