Browsing by Author "Suwargadi, B"

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    Post-glacial coupling of the Australasian monsoon and teleconnections to the North Atlantic: new insights from Indonesian speleothems
    (GNS Science, 2009-05-15) Griffiths, ML; Drysdale, RN; Gagan, MK; Zhao, JK; Ayliffe, LK; Hellstrom, JC; Hantoro, WS; Frisia, S; Feng, YX; Cartwright, I; St Pierre, E; Fisher, M; Suwargadi, B
    The Australasian monsoon system orchestrates rainfall variability and terrestrial productivity in the densely populated region of the tropical Indo-Pacific. A clear understanding of the dominant mechanisms governing its variability has been difficult to resolve, partly because we currently lack high-resolution proxy records of past monsoon behaviour, particularly for the southern tropics. Here we provide a radiometrically dated reconstruction of Australian-Indonesian summer monsoon (AISM) rainfall based on oxygen isotopes and trace element data in stalagmites from southern Indonesia. The multi-proxy records are tied to age-depth models constructed from 62 TIMS and MC-ICP-MS U-series ages, covering the period 0 to 12.6 ka B.P. The record shows that the AISM was anti-phased with the East Asian summer monsoon (EASM) on orbital to millennial-centennial timescales over the past 12.6 ka. At the orbital-scale, local summer insolation was an important driver of opposing changes in AISM and EASM rainfall. However, a slight mismatch between the AISM and insolation from 9 to 11 ka B.P. is concurrent with the sharp rise in eustatic sealevel, which apparently increased the supply of northwesterly summer monsoon moisture to the Indonesian maritime continents. At millennial-centennial timescales, the oxygen isotope and trace element records show that periods of weakened North Atlantic meridional overturning circulation and cooling, including the Younger Dryas cold stage, are in phase with sharp increases in AISM rainfall. The connection between the AISM and a cooler North Atlantic is probably due to enhanced outflow from the Asian winter monsoon and associated southward migration of the intertropical convergence zone. These interhemispheric connections were dominant until ~6.5 ka, when the El Niño-Southern Oscillation became the governing influence on AISM variability.
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    What drives vegetation changes in South Sulawesi during the MIS 5e transition?
    (Copernicus Publications, 2024-04-17) Kimbrough, A; Gagan, MK; Dunbar, GB; Treble, PC; Hantoro, WS; Zhao, JX; Edwards, RL; Shen, CC; Suwargadi, B; Wong, HKY; Rifai, H
    Sulawesi speleothem carbon isotopes (δ13C) are found to co-vary with deglacial warming and atmospheric CO2 measured from Antarctic ice cores. This co-variation has thus far been attributed to speleothem δ13C recording changes in vegetation productivity and microbial activity in the soils overlaying caves as vegetation and microbes respond to glacial-interglacial changes in temperature and atmospheric CO2 (Kimbrough et al., 2023; Krause & Kimbrough et al., in press). However, the relationship between speleothem δ13C and regional environmental change is complex and deconvolving the effect of different environmental drivers is difficult. To further investigate the ecosystem response in the Indo-Pacific Warm Pool to substantial warming and CO2 rise during the penultimate deglaciation/marine isotope stage 5e (~127 kyrs ago) we use complimentary geochemical proxies extracted from stalagmite CaCO3. These proxies include phosphorus and sulphur which respond to nutrient uptake by forest biomass above the cave (Treble et al., 2016). The relative abundance of metals such as copper, iron, zinc, and lead are assessed as another means to track biomass/soil regeneration via selective element delivery to the stalagmites by organic colloids flushed from the soil zone (Borsato et al., 2007). These vegetation proxies are compared with the speleothem δ13C and δ18O records and corresponding high-resolution fluorescence mapping of organics via confocal laser scanning (fluorescence) microscopy (Sliwinski & Stoll, 2021). The comparison of transition metals to stable isotopes (δ18O, δ13C) in the Sulawesi speleothem records makes it possible to distinguish between periods in the record where vegetation productivity increased in response to a rise in temperature and CO2 verses periods where changing hydroclimate played a more dominant role. Characterising the appropriate drivers and proxy response is critical to accurately interpret tropical paleoclimate records where interpretations rely on assumptions that rainfall is the primary driver of vegetation change. © Author(s) 2024. This work is distributed under the Creative Commons Attribution 4.0 License.