A 14 000-year record of paleoenvironmental change in the western basin of China's third largest lake, Lake Taihu

Abstract

The longest vertical profile from the western basin of Taihu Lake ever taken was nearly 4 m (396 cm) in length and represented a time period of over 14 000 years. The core was analyzed for the following proxies, magnetic susceptibility, organic carbon isotope, total organic carbon, total nitrogen, total pigments, saturated hydrocarbons, carbon 14, thermolytic hydrogen (the hydrogen index, HI) and foraminifera. Results from the west Taihu lake core indicate that ca. 14 300–13 400 a B.P., the lake was relatively shallow and the climate was likely to have been quite arid. From 13 400 to 12 400 a B.P., the environment became less arid and the depth of the water in Lake Taihu increased. Marine incursions occurred during this period as indicated by the presence of numerous marine foraminifera. From ca. 12 400 to 10 900 a B.P., the climate became wetter, warmer and more variable. A cold dry period occurred around ca. 11 500 a B.P., causing the lake to become more shallow. From 10 900 to 10 000 a B.P., a warm and wet period reasserted itself and water depth again increased. A cold dry period reoccurred from 10 000 to 9500 a B. P. From 9500 to 7200 a B.P., the climate was quite variable. By 7200–5700 a B.P., the climate again turned warmer and wetter. Some of the major sediment proxies used in this study changed dramatically at ca. 5050 a B.P., reflecting changes in material source and a probable interruption of sedimentation. The modern environment (4900 aB.P.-present) was characterized by a well oxidized sediment layer and thriving algae. The lake is presently very eutrophic and is characterized by cyanobacteria, primarily Microcystis aeruginosa, the dominant primary producer in the lake. This is the first study to use a variety of organic geochemical proxies to infer paleoenvironmental changes in Taihu Lake.