Late Quaternary peat formation and vegetation dynamics in a lowland tropical swamp; Nee Soon, Singapore

Abstract

Cores of sediment from Nee Soon, a peat-forming freshwater swamp located in the perimarine zone of Singapore, have yielded a record of vegetation history that comprises parts of the last glacial and Holocene periods. The evidence includes two conventional and four AMS radiocarbon dates, the oldest of which is 23,050±330 B.P. (uncalibrated radiocarbon years), and variations in the abundances of sub-fossil pollen and spores and charcoal. The results of a study of the relationship between contemporary vegetation and modern pollen accumulation facilitated interpretation of sub-fossil tree pollen data. Peat formation occurred at Nee Soon during the last glacial, when sea levels on the Sunda continental shelf were well below those at present. The occurrence of montane pollen types, notably Podocarpaceae, in sediment samples dated to the late glacial and early Holocene suggests either temperatures substantially lower than those of the present and, possibly, humid conditions, or cold, seasonally dry climates and reduced levels of atmospheric CO 2. The abundance of charcoal indicates the widespread occurrence of fires throughout the entire period represented by the cores. For the mid Holocene, the evidence indicates an increased saline influence, presumably as a result of relatively high sea levels. Falling sea levels during the late Holocene appear to have preceded the onset of the most recent period of peat formation at Nee Soon. The evidence confirms that long (last glacial–interglacial) records of lowland vegetation history are available from terrestrial locations in the humid core of Southeast Asia and suggests that the complexity of perimarine swamp dynamics is not captured fully by Anderson's model, which assumes a close relationship between peat formation and sea level.