Holocene oxygen isotope record of diatoms from Lake Kotokel (southern Siberia, Russia) and its palaeoclimatic implications

Abstract

The oxygen isotope composition of diatom silica (δ18Odiatom) from marine and lake sediments is helpful for the interpretation of the past climate and environments, especially when complemented by other proxy records. This paper presents a Holocene oxygen isotope record of diatoms from Lake Kotokel, located 2 km east of Lake Baikal in southern Siberia, Russia. The isotope record displays variations in δ18Odiatom from +23.7 to +30.3‰ from about 11.5 ka BP until today. Comparing the isotope composition of recent Lake Kotokel water (mean δ18O = −12‰) to that of the most recent diatom sample (δ18O = +27.5‰), an isotope fractionation in the right order of magnitude was calculated. The Kotokel δ18O diatom record is controlled by changes in the isotopic composition of the lake water rather than by lake temperature. Lake Kotokel is a dynamic system triggered by differential environmental changes closely linked with various lake-internal hydrological factors. A continuous depletion in δ18O of 6.6‰ is observed from early to late Holocene, which is in line with other hemispheric environmental changes (i.e. a mid- to late Holocene cooling). Enhanced evaporation effects and higher relative supply from a southeasterly moisture source explain the relatively heavy isotopic composition in a rather cold early Holocene. In summary, changes in the Holocene δ18O diatom record of Lake Kotokel reflect variations in δ18O of precipitation linked with both air temperatures (Tair) as well as evaporation effects and, to a lesser degree, meltwater pulses from the mountainous hinterland and changing atmospheric moisture sources.