Variations in Isotopic Compositions (18o, 13c, 15n) of Paleolake Sediments From the Shufan Plateau as Indicators of Environmental Changes During the Holocene

For the first time, isotopic compositions of total carbon (δ13Ctotal) and nitrogen (δ15Ntotal) for organogenic deposits and isotopic compositions of oxygen (δ18Ocell.) with carbon (δ13Ccell.) for cellulose from the Holocene organogenic deposits were studied for the southern Far East of Russia. The study focused on the section of lacustrine-boggy deposits of the Shufan Plateau (Southern Primorye), which accumulated during 9720 cal. yr BP. The greatest variability of isotope ratios was determined for the early Holocene and the last thousand years. Effects on the isotopic composition of such factors as hydroclimatic changes, including the dynamics of the hydrological regime of the paleolake around which a pet bog developed, the botanical composition of peat-forming plants, and peat accumulation rates were analyzed. An increase in moisture had different effects on isotopic fractionation in the peat composed of bryophytes and vascular plants. The age was determined and positive and negative peaks of stable isotope values were interpreted and compared with the data for the region. One of the leading factors of isotope fractionation was moisture changes associated with monsoon circulation. It is suggested that isotope ratios may be influenced by a decrease in lake depth, evaporation, and snow contribution to groundwater recharge. The comparison of δ13Ctotal, δ15Ntotal records and C/N ratios down-section revealed periods with different degrees of organic matter degradation. Direct correlations were established for the δ13Сcell. and δ18Оcell. values and inverse correlations for the δ13Сtotal and δ15Ntotal values, which change regularly in different-age peat generations. Changes were identified in the isotopic composition of peat and turf formed after the Little Ice Age in warmer conditions and under increasing anthropogenic influence.