The analysis of oxygen isotopes from diatom silica in sediment cores has reached importance for reconstructing the paleoclimate and is especially valuable in non-carbonate lakes of cold regions, where no other bioindicators are present. A new approach for samples in sub-mg range has been developed to provide a better chronological resolution and to expand the method to periods where less biogenic silica is available. Sample material from Lake Elgygytgyn will be analysed and a &#948;18O curve of the last 280.000 years will be generated to add a strong climate proxy to the various analysis performed so far. The Lake lies inside a meteorite impact crater of about 18 km in diameter which was formed approximately 3.6 million years ago. 50 streams are draining into this cold, oligotrophic lake from within the crater rim whereas only one outlet stream is present. Hence, the lake offers a unique option to fill the spatial gap of locations in the Arctic where paleoclimate reconstructions are rare. Former drilling operations show that the lake could contain the longest, most continuous terrestrial record of past climate change in the entire Arctic back to the time of impact (Brigham-Grette, 2006).The analysis aims on the planktonic Cyclotella ocellata-complex which is persistent through a variety of climate conditions and present throughout the core (Cherapanova, 2006). Another goal is to examine a possible species-dependent fractionation by comparing the mentioned complex with Pliocaenicus costatus var. Sibiricus in the holocene. After extracting the diatoms from sediment cores with various preparation steps a minimum of ~700µg fine material from 5 g of wet sample is required. A bead is melted and reacted with a CO2 laser under BrF5 atmosphere. The oxygen is then transferred to the mass spectrometer and compared with a reference standard of known isotopic composition. Specially designed software and a video camera are used to survey and record the process in the reaction chamber and allow an automised, remote operation. Tests on standard material (NBS 28, Campolungo) showed a standard deviation <0.2. First results will be presented at the meeting. The expected results will be the base for studying the climate history using stable isotopes in lacustrine diatoms of the whole 300 m sedimentary sequence on sediment cores at Lake Elgygygtgyn to be drilled within the frame of the ICDP in 2009.