Palaeoenvironmental developments in the Lake Tondano area (N. Sulawesi, Indonesia) since 33,000 yr BP

Geo(morpho)logical, sedimentological. and ecological developments in the Lake Tondano area since +/- 33,000 yr BR, and limnological changes in the moderately-sized lake situated at 680 m asl in the northern part of Sulawesi, Indonesia are discussed. First, the environmental setting of the lake is presented. Study of the regional distribution of lacustrine sediments, and a detailed analysis of their sedimentary facies (texture, organic matter content) suggest major changes in size and depth of the lake and in past sedimentation. Insight into the long-term development of the lake (sedimentation processes) is highly relevant for sustainable use of the present lake. Analysis of diatom assemblages provides further detail of the changing aquatic settings of the lake; lake levels rise quickly around 33,000 and 12,000 yr B.P., fall dramatically between +/- 30,000 and 13,000 yr B.P. and are lowered gradually since approximately 6000 yr B.P., following Early Holocene high lake levels. Drainage of the lake is affected by both volcanic depositional events and regional climatic events. Palynological analysis is indicative of local palaeoecological settings in the lake area and regional climatic change; a distinct, Late Pleistocene phase, with lower precipitation and lowered mean temperatures is inferred. Furthermore, progressive deforestation of the Tondano uplands is evident, as well as diffuse anthropogenic/volcanic vegetation disturbance from the early Mid Holocene onwards. Information from sedimentary facies, diatom assemblages and local palaeoecology (pollen) are integrated to reconstruct palaeoenvironmental settings and processes in the lake area. This record of environmental change as well as the pollen-based record of regional vegetation and climate change corroborates other palaeoenvironmental data derived from the few terrestrial sites in the region, The data attribute a greater magnitude of temperature and precipitation change in the region than is commonly deduced in studies based on marine faunal and sedimentary records. The Lake Tondano sedimentary record is highly suitable for further analysis aimed at determining the exact timing and amplitudes of environmental change in the SE Asian equatorial region. (C) 2001 Elsevier Science B.V. All rights reserved.