Browsing by Author "Blaauw, M"

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    A northward shift of the southern westerlies during the Antarctic cold reversal: evidence from Tasmania
    (Australasian Quaternary Association, 2018-12-10) Alexander, J; Fletcher, MS; Pedro, JB; Mariani, M; Beck, KK; Blaauw, M; Hodgson, D; Heijnis, H; Gadd, PS; Lisé-Pronovost, A
    The Last Glacial Termination (LGT) was interrupted in the Southern Hemisphere by the Antarctic Cold Reversal (ACR; 14.7 to 13 ka), a millennial-scale cooling event that coincided with the Bølling– Allerød warm phase in the North Atlantic (14.7 to 12.7 ka). This inter-hemispheric asynchrony of climate change through the LGT, the bipolar seesaw, has been theoretically linked to latitudinal shifts in the southern westerly wind belt (SWW) and their proposed influence over the global carbon cycle via wind-driven upwelling of CO2 rich deep waters in the Southern Ocean (SO). However, while climate models and theory predict a northward shift of the SWW during the ACR in response to ocean-atmosphere heat dynamics, proxy-based reconstructions disagree on the behaviour of the SWW through this interval, and the role of the SWW during the LGT remains contested. Here we present terrestrial proxy palaeoclimate data (pollen, μXRF geochemistry, charcoal) from multiple lakes across Tasmania (40-44⁰S), an island located at the northern edge of the SWW. Our data reveal a clear SWW increase over Tasmania during the ACR, synchronous with reduced SWW-driven upwelling in the SO at the southern edge of the SWW. When combined with evidence from Antarctic ice cores and terrestrial records from New Zealand and Patagonia our results suggest a hemisphere-wide migration of the SWW during the LGT, lending support to the hypothesis that changes in wind-driven ventilation of CO2 from the Southern Ocean were a key driver of the global carbon cycle during the LGT. © The Authors.
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    Scientific drilling of sediments at Darwin Crater, Tasmania
    (Copernicus Publications, 2019-06-12) Lisé-Pronovost, A; Fletcher, MS; Mallett, T; Mariani, M; Lewis, RJ; Gadd, PS; Herries, AIR; Blaauw, M; Heijnis, H; Hodgson, DA; Pedro, JB
    A 70 m long continental sediment record was recovered at Darwin Crater in western Tasmania, Australia. The sediment succession includes a pre-lake silty sand deposit overlain by lacustrine silts that have accumulated in the ∼816 ka meteorite impact crater. A total of 160 m of overlapping sediment cores were drilled from three closely spaced holes. Here we report on the drilling operations at Darwin Crater and present the first results from petrophysical whole core logging, lithological core description, and multi-proxy pilot analysis of core end samples. The multi-proxy dataset includes spectrophotometry, grain size, natural gamma rays, paleo- and rock magnetism, loss on ignition, and pollen analyses. The results provide clear signatures of alternating, distinctly different lithologies likely representing glacial and interglacial sediment facies. Initial paleomagnetic analysis indicate normal magnetic polarity in the deepest core at Hole B. If acquired at the time of deposition, this result indicates that the sediment 1 m below commencement of lacustrine deposition post-date the Matuyama–Brunhes geomagnetic reversal ∼773 ka. © Author(s) 2019.
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    What happened at the end of the mid-Pleistocene transition in the Southern Hemisphere? Insights from western Tasmania, Australia
    (International Union for Quaternary Research (INQUA), 2019-07-30) Fletcher, MS; Lisé-Pronovost, A; Mallett, T; Mariani, M; Cooley, S; May, JH; Gadd, PS; Herries, A; Blaauw, M; Heijnis, H; Hodgson, DA; Pedro, JB
    The current southward shift in the southern westerlies that is stripping southern Australia of rainfall is unprecedented over the past 12 kyrs years at least, and is due to the effects of both the anthropogenic hole in the ozone layer and greenhouse gas-driven global warming. Predictions of future climate suggest the Earth is moving in to a “super-interglacial” (peak warming) because of anthropogenic greenhouse gas release. “Super-interglacials”, which are warmer than today, are uncommon in the geological record. A recent increase in the frequency of these peak warming events since ca. 450 ka (the end of the mid-Pleistocene transition; MPT) is associated with a 7° latitude southward shift of the southern westerlies and an increase in atmospheric CO2 that warmed the atmosphere - a stark similarity to current trends. Here, we present multi-proxy analyses of two closely spaced (<50 km) sediment cores that comprise a complete sequence from the mid-Pleistocene to the present from western Tasmania, Australia - in the mid-latitudes of the Southern Hemisphere. Lake Selina is a modern-day lake with a continuous ca. 230 kyr sediment sequence, while Darwin Crater is a palaeo-lake within a meteorite impact crater that formed at ca. 816 ka and which completely in-filled during MIS5 (ca. 120 ka). We report on petrophysical whole core logging, lithological core description, spectrophotometry, grain size, natural gamma ray, paleo- and rock-magnetism, loss-on-ignition, pollen analyses and micro-XRF geochemisrty. The composite record is unique in the Australian sector of the Southern Hemisphere and we discuss the data in the context of the global and regional changes that occurred at the end of MPT, paying particular attention to impact of the shift toward warmer super-interglacials, the large-scale southward shift of the southern westerlies and higher atmospheric CO2 content that occurred at ca. 450 ka (MIS11 to present).