Browsing by Author "St Pierre, E"

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    Human impact on the environment in Western Flores, Indonesia during the late Holocene: identifying agricultural transitions
    (18th INQUA Congress, 2011-07-21) St Pierre, E; Zhao, JX; Aplin, K; Drysdale, RN; Golding, SD; Griffiths, ML; Hua, Q
    Limestone caves can act as excellent repositories of palaeoenvironmental information and past human activities. This paper presents a multi-proxy record of late Holocene palaeoclimate and palaeoenvironmental change derived from environmental archives in Liang Luar (Steam Cave), western Flores, Indonesia. Liang Luar, located ~1 km from Liang Bua (the discovery site of the hominid species Homo floresiensis), is a ~1.6km long passage with several large chambers and numerous speleothems (stalagmites and stalactites). A palaeoclimate record was compiled using stable carbon and oxygen isotope ratios from a stalagmite precisely dated to 0-1800 yr BP using U/Th dating. The stalagmite isotope record preserves an episode of rapid vegetation change c. 800 yr BP marked by a large shift in carbon and decoupling of the carbon from the oxygen isotopes, and thus thought to be unrelated to climate. Excavated owl pellet deposits in the entrance of Liang Luar dated by 14C AMS on charcoal, reveal continuous sediment deposition from at least 2400 yr BP to the present. The 14C chronology demonstrates a sudden increase in depositional rates at the cave entrance as well as an increase in the abundance of charcoal fragments, at the time of the vegetation change inferred from the stalagmite record. Faunal remains indicate the commensal species Rattus exulans, arrives early in the sequence, while Rattus rattus appears much later. A surprisingly late appearance of two rodents associated with irrigated rice fields, together with a surge in frog remains, indicates wet rice farming was only recently introduced to the area. These paleoenvironmental records act as a basis from which to understand the timing and intensity of human impacts on late Holocene environments in western Flores, and the relationship of this incursion to changing land use patterns. Copyright (c) 2011 INQUA 18
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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 NiƱo-Southern Oscillation became the governing influence on AISM variability.