LAKE EVOLUTION HISTORY AND CLIMATE CHANGE OVER THE PAST 230 KYRS FROM MAAR LAKE TIANYANG, TROPICAL SOUTH CHINA

Two parallel and long lacustrine cores TY1(225m) and TY2(230m) were collected from the center of dry maar Lake Tianyang in tropical South China (20°ã31¢N, 110°ã18¢E). Its sediment keeps continuous, high-resolution archives for past climate changes and lake evolution history. The two cores' lothology are same, including three parts: the bottom basalt part(below 224m), the middle diatomite part intercalated with clay(224-34m) and an exception of peat sediment at 38-34m, and the upper alluvial sediment part(34-0m). The K-Ar and TL age of the bottom basalt of Core TY1 was about 470 kyr BP. The lake sediment records a history of about 400 kyr(Zheng, 1999). Diatom analyses are made on the upper 130m depth of Core TY2. The variations of diatom species composition and their relative contents reveal the limnological and climatic changes over the past 230kyr. During MIS7a-d(130-100m), MIS6(100m-75m) and MIS4-3(75-34m), the lake and climate condition was quite unstable; while during MIS 5, the lake and climate condition was quite stable. Aulacoseira granulata was the dominant diatom species during MIS7-3, accompanied by A. granulata var. angustissima, Cyclotella meneghiniana, C. stelligera, C. stelligera var. tenuis during MIS 7-6, and by Fragilaria etc attached and benthic diatom species during MIS3d. During warm-hot MIS7, oligotrophic conditions turned into mesotrophic conditions, at the same time eutrophic conditions are alternated with oligotrophic conditions; pH are mainly neutral to alkaline with occasional slightly acid conditions. During cool MIS6, mesotrophic conditions turned to oligotrophic conditions. Warm-hot MIS5 were always in mesotrophic condition with only very little fluctuation. During cool MIS4-3, the abundance of diatom dramatically decreases and reaches to nearly zero above the core depth of 34m. During the 34-130m period eutrophic periods are exactly corresponding with acid periods, and alternating with oligotrophic periods. All these indicate that the climate in South China during the last 230 kyr were warm-wet and cool-dry. During MIS6-5 Tianyang maar was a shallow-water lake, and during MIS 4-3 it firstly changed into marsh characterized by abundant attached and benthic diatom species, and then completely dry during the cool-dry MIS3d period. * It is supported by Project CAS KZCX2-SW-118, NSFC 40002012.