Re-examination of the temperature-dependent relationship between δ18Odiatoms and δ18Olake water and implications for paleoclimate inferences

International audienceThe oxygen isotope composition (d 18 O) of diatoms is commonly used for paleoclimate reconstruction. There is, however, no consensus regarding the equilibrium isotopic fractionation factor between diatom silica and the water in which it is precipitated. We reexamined the temperature-dependent relationship between d 18 O diatoms and d 18 O lake water from Lake Annecy (France). A temperature coefficient of-0.16%/°C (R 2 = 0.51) was determined , supporting findings from previous calibration studies. However, regression lines obtained from different calibration studies, though displaying similar slopes, were shifted. In this manuscript, we propose that several factors, including selected variables (temperature, d 18 O lake water), analytical techniques, the impact of diagenetic processes and biological effects, may influence the silica-water fractionation factor for diatom silica. The similar magnitude of the diatom-temperature coefficients determined across studies is promising, supporting its use as a valuable tool for interpreting variations in d 18 O values from fossil lacustrine diatoms in temperate lakes. With respect to paleoclimatic applications , the temperature-dependent relationship yielded uncertainties of ±3°C on reconstructed temperatures and ±0.5% on d 18 O lake water