Holocene monsoon changes inferred from lake sediment pollen and carbonate records, northeastern Cambodia

Major Holocene monsoon changes in continental Southeast Asia are reconstructed from analysis of C-14-dated changes in pollen and organic/inorganic carbon in sediment cores taken from permanent, closed-basin, volcanic lakes in Ratanakiri Province, northeastern 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 retrieved from Kara Lake, representing the last 9300 years, shows that the late Glacial conditions ended about 8500 C-14 yr B.P., more than 1000 years later than sites in southwest China. Summer monsoon intensity increased over the period ca. 8400-5300 C-14 yr B.P., similar to most other sites in the Asian monsoon region. A subsequent expansion of secondary forests at the expense of dense semievergreen forests suggest a drier climate leading to more frequent fire disturbance. After ca. 3500 C-14 yr B.P. disturbance frequency may have increased further with increasing seasonality. From ca. 2500 C-14 yr B.P. 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. (C) 2001 University of Washington.