Combined wood cellulose extraction method for radiocarbon and stable isotope analysis

The combination of tree-ring radiocarbon (¹⁴C) and stable isotope ratios of carbon, oxygen, and hydrogen has been proposed as a valuable approach to solve dating uncertainties in this period and is therefore a helpful tool for reconstructing Late Glacial climate conditions. However, sample throughput at annual to sub-annual resolution remains limited by current wood pretreatment methods, as no established protocol exists that is suitable for both ¹⁴C and stable isotope analyses, given their distinct requirements (i.e., ultra-clean cellulose for ¹⁴C analysis, preservation of original isotopic signatures and cellulose homogeneity for stable isotope analysis). Additionally, Late Glacial subfossil wood often suffers from degradation, resulting in lower cellulose content compared to modern wood. Here, we introduce a novel cellulose extraction method suitable for both ¹⁴C and stable isotope measurements, thereby reducing labor intensity and substantially increasing analytical throughput of multiproxy analyses. The new method was systematically evaluated using both modern and Late Glacial subfossil wood and benchmarked against established reference protocols optimized specifically for either ¹⁴C or stable isotope analyses. Two major modifications were introduced: (1) the addition of a strong base step to isolate the alpha cellulose fraction, and (2) modified reaction times for both base and bleaching steps. We present preliminary results with a special focus on preservation of isotopic (¹⁴C, ¹³C, and ¹⁸O) signatures and cellulose yield. The feasibility of the new cellulose extraction method for multiproxy analysis is discussed, along with remaining challenges and directions for further optimization.