C-13 AND N-15 ABUNDANCES IN THE SEDIMENT CORE (VER92 1-ST-10-GC2) FROM NORTHERN LAKE-BAIKAL/

Carbon and nitrogen stable isotope compositions of organic matter, TOC /TN ratio, and manganese concentration in a sediment core that was col lected in northern parr of Lake Baikal (VER92ST10-GC2, water depth at 922 m, about 3 m long) were investigated to elucidate the origin of th e sedimentary organic matter and its associated environmental factors. The sediment core was composed of mainly two parts: turbidite section s and other sections. Constant delta(13)C and delta(15)N values of the rurbidite sections were observed (-26.8 +/- 0.2 parts per thousand, f or delta(13)C and 3.2 +/- 0.1 parts per thousand for delta(15)N) throu ghout the core. The higher delta(13)C in turbidite sections (about -27 parts per thousand) than that of the other sections (-31 to -29 parts per thousand) was clearly observed, and delta(15)N was different betw een turbidite sections (about 3 parts per thousand) and other sections (3 to 5 parts per thousand). delta(13)C of Other sections was close t o that of pelagic phytoplankton, indicating that sediment other than t urbidite sections is composed of autochthonous components. The variati on of stable isotopes in other sections may be possibly caused by the changes in either phytoplankton growth rate or contribution ratios of terrestrial to aquatic plants for delta(13)C. Either denitrification o r fluctuation of delta(15)N in pelagic phytoplankton can be the cause of variable delta(15)N in other sections.