Universität zu Köln

The objectives were

• to process a 250ka ?¹⁸O record for the upper part of the 16.5m long core (LZ1024) from Lake El’gygytgyn with concrete paleoclimate interpretation.
• to compare the results from this record to local, regional and global climate archives and ?¹⁸O records.
• to evaluate sub-surface sample material from Lake El’gygytgyn, NE Russia for possible species-dependent fractionation effects and compare their ?¹⁸O values to the oxygen isotope composition of the lake and its inflow streams.
• to investigate the efficiency of a preparation protocol adapted to the <10 µm fraction for sediment samples from Lake El’gygytgyn.

Although ?¹⁸O records from ice-cores and foraminifera are among the most important paleoclimate records only eight laboratories world-wide (including AWI) are able to analyse the ?¹⁸O in biogenic silica which have never been compared. This shortage is mainly due to methodological aspects and challenges. Generally, the complexity of the analysis itself from preparation to instrumentation already complicates and even often inhibits the application of this valuable proxy. All of these questions need to be addressed to guarantee an improved analysis for gaining higher-resolution ?¹⁸O records with enhanced reliability.

Hence, additional objectives and aims of this thesis are:

• to assess the usefulness of various chemical and optical contamination assessment methods and correction techniques to calculate ?¹⁸O_corr from ?¹⁸O_measured.
• to establish a new, easy and fast routine for removing the exchangeable hydrous components within biogenic silica before the oxygen isotope analysis.
• to develop a new, safer, faster and semi-automated online approach for analysing oxygen isotopes in biogenic silica since most analytical techniques available are timeconsuming and labour-intensive.
• to examine if the same analytical methods applied in different laboratories provide reproducible ?¹⁸O results.
• to test if the four different methods compensating for the exchangeable oxygen performed in the eight different laboratories active within this field of research result in accurate and reproducible ?¹⁸O values.
• to establish new biogenic silica working standards covering a large range of ?¹⁸O values that can be distributed within the biogenic silica community. Up to now, only one official quartz standard and internal biogenic standards exist.