A continuous record of climate changes of the last 5 million years stored in the bottom sediments of Lake Baikal

The paper considers the first results of investigation of the cores obtained by drilling in Lake Baikal on the top of the underwater Akademichesky Ridge in 1996. Two boreholes, one to a depth of 300 m, and the other to a depth of 100 m below sediment surface were drilled at 53 degrees 41'48" N-108 degrees 21'06" E at a point where the depth of the lake is 321 m. Akademichesky Ridge separates the middle and the northern basins of Lake Baikal. Its top is 500 m above the bottom of the northern basin, and more than 1000 m above the bottom of the middle basin. The ridge is covered by sediments that are 1000-1500 m thick. The core was collected down to 200 m in the first borehole, and totally in the second one. Yield of the cores was more than 95 %. Sediments consist of terrigenic and biogenic silts. All along the section, clay layers alternate with layers of diatomaceous silt. Studies of the section revealed that sediments accumulated under deep water during all the period of their deposition; no hiatuses or unconformities were found. Studies done in Russia, USA, Japan and Germany gave results that are consistent with each other. Correlation of magnetic properties with the paleomagnetic scale revealed that the age of sediment at 200 m is 5 My. Mean sediment accumulation rate was constant and equaled 4 cm per 1 ky. Rhythmic structure of the sediments consisting of layers of diatom-barren clays and diatomaceous silts is due to cyclic changes of cold and warm climates. Changes in the abundance of diatom algae frustules is accompanied by changes in the concentration of biogenic silica, magnetic susceptibility, water content, and wet density. The vertical profiles of these parameters perfectly correlate with the act oceanic delta(18)O SPECMAP curve. Hence, the first continuous record of the paleoclimates of Central Asia for Pliocene and Pleistocene has been obtained. This record may serve a basis to study climate changes more detail.