In my first PhD year I participated in a helicopter expedition undertaking an ecological and limnogeological survey of 14 thermokarst lakes along a north-south transect (73°-69°N) along the western side of the lower Lena river. The aim is to reconstruct the Holocene palaeoenvironmental history of north-east Siberia using diatoms combined with sediment-geochemical features.The poster presents sedimentological aspects from the study of El'gene Kyuele (71°18,04' N, 125°34,15' E, length 2.9 km, width 0.5 km, max. water depth >5 m). The lake is about 50 km north of the present treeline and is built by thermokarst processes of the surrounded deeply loesslike Yedoma sediments. To gain informations about the sediment source and the influence of erosion geochemical and grain-size studies were conducted on El'gene Kyuele sediment core PG1975-1 (core length 136 cm, basal age 6792 ± 30 14C years BP). Downcore elemental composition of PG1975-1 have been analysed using an Avaatech XRF Core Scanner at AWI Bremerhaven. In this study we apply XRF data (Sr/Rb, Zr) as a grain-size proxy. For correlation of the downcore elemental composition to silt and clay content grain-size is currently under examination using a Laser Diffraction Particle Analyser at AWI Potsdam. Due to PG1975-1 not containing any diatoms for unknown reasons other sediment cores from transect lakes (PG1972-1 and PG1984), providing divers diatom flora, are brought into the PhD project. Additionally we plan a follow-on expedition (Lena 2010) to retrieve sediment cores from Lake El'gene Kyuele and the newly selected Lake Ozero Kyutyunda which is 25 km north-west from the side of PG1984 providing sediment material for comparative palaeolimnological research.