| Abstract: |
Major Holocene monsoon changes in continental Southeast Asia are reconstructed from analysis of 14C-dated changes in pollen and organic/inorganic carbon in sediment cores taken from permanent, closed-basin, volcanic lakes in Ratanakiri Province, north-eastern Cambodia. Analysis focuses on the nature and timing of monsoon changes, inferred from changes in vegetation and lake conditions. These data provide the first well-dated palynological record covering most of the Holocene and continuous up to the present, from a terrestrial site in mainland Southeast Asia. The record from a 15-m core retreived from Kara Lake, representing the last 9300 years, shows that the late Glacial conditions ended about 8500 14C yr. B.P., more than 1000 years later than sites in southwast China. Summer monsoon intensity increased over the period 8400-5300 14 C yr B.P., similar to most other sites in the Asian monsoon region. A subsequent expansion of secondary forests at the expense of dense semi-evergreen forests suggest a drier comate leading to more frequent fire disturbance. After 3500 14 C yr BP disturbance frequency may have increased further with increasing seasonality. from ca. 2500 14C yr BP to the present, dense forest has recovered in a mosaic with annually burned dry forest, but climate may not be the main control on local vegetation dynamics in the late Holocene.
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