Reconstructing the Australasian monsoon over the last 40,000 years using speleothems and palaeoclimate modelling
Deep atmospheric convection over the western equatorial Pacific occurs at the junction of the rising limbs of the meridional Hadley cells and the Pacific Walker circulation, making it one of the most atmospherically dynamic regions on Earth. Here, interactions between the Australasian monsoon and at...
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| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
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| Online Access: | http://hdl.handle.net/1885/104839 https://doi.org/10.25911/5d778b6757cc6 https://openresearch-repository.anu.edu.au/bitstream/1885/104839/4/Krause%20Thesis%202016.pdf.jpg |
| Summary: | Deep atmospheric convection over the western equatorial Pacific occurs at the junction of the rising limbs of the meridional Hadley cells and the Pacific Walker circulation, making it one of the most atmospherically dynamic regions on Earth. Here, interactions between the Australasian monsoon and atmospheric convection result in highly variable regional precipitation patterns across different latitudes. The dynamics of the Australasian monsoon over the past ~40,000 years are relatively well understood at its northern limit (the East Asian Summer Monsoon), but less well known for its southern limit (the Indo-Australian Summer Monsoon). In the equatorial region however, even less is known about the past behaviour and dynamics of this major system. Here we present a new, continuous, absolutely dated speleothem record from southwest Sulawesi, Indonesia that spans the past 40,000 years. Isotopic ratios of oxygen (δ18O) and carbon (δ13C) in the speleothem calcite were analysed at ~50-yr resolution to reconstruct rainfall amount and vegetation productivity. The records show that the strength of regional deep atmospheric convection is primarily controlled by sea level via the exposure and inundation of the Sunda Shelf. This sea-level control results in a relatively dry last glacial period that was terminated by the onset of deglaciation and the inundation of the Sunda Shelf, which abruptly increased the intensity of deep atmospheric convection. The Sulawesi speleothem δ18O record does not capture millennial-scale variability in response to North Atlantic Heinrich events, in contrast to nearby speleothem records from Borneo and Flores. To explore this observation, the climatic impact of Heinrich events in the western equatorial Pacific region was simulated using idealised North Atlantic freshwater hosing experiments performed with the HadCM3 and CSIRO Mk3L general circulation models. Precessional forcing is shown to influence the manifestation of Heinrich events, particularly across the Southern Hemisphere via the ... |
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