Palaeo-seasonality of the last two millennia reconstructed from the oxygen isotope composition of carbonates and diatom silica from Nar Gölü, central Turkey

Carbonates and diatoms are rarely deposited together in lake sediments in sufficient quantities for the oxygen isotope composition (δ¹⁸O) to be investigated simultaneously from both hosts. Here, δ¹⁸O_carbonate are compared to δ^18O_diatom data from the varved sediments of Nar Gölü, a closed lake in central Turkey, over the last 1710 years. Lake monitoring suggests carbonate is probably precipitated during May–June and δ¹⁸O_carbonate is a proxy for regional water balance. Diatom activity is mainly weighted towards the spring. At times between ∼301 and 561 AD, while δ¹⁸O_carbonate values are the highest for the entire 1710 year period, suggesting summer drought, δ¹⁸O_{corrected-diatom} values are among the lowest. δ¹⁸O_lakewater values estimated for the times of diatom growth and carbonate precipitation show large differences. We suggest this could be explained by increased snowmelt that formed a freshwater lid on the lake at the time of peak diatom growth. Increased snowmelt is also inferred ∼561–801 AD. From 801 AD to the present, precipitation is less winter-dominated, although increased snowmelt is inferred 921–1071 AD and in the latter part of the Little Ice Age (i.e. the mid to late 1800s AD). By combining oxygen isotope data from hosts that form in lakes at different times of the year, we show that such analyses can provide insights into palaeo-seasonality.