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, δ18Ocarbonate are compared to δ18Odiatom 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 δ18Ocarbonate is a proxy for regional water balance. Diatom activity is mainly weighted towards the spring. At times between ∼301 and 561 AD, while δ18Ocarbonate values are the highest for the entire 1710 year period, suggesting summer drought, δ18Ocorrected-diatom values are among the lowest. δ18Olakewater 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. ► Comparing δ18O from carbonates and diatoms allows insights into seasonality. ► Use of data from lake monitoring to help interpret down-core isotope variations. ► Severe winters inferred 301–801 AD, 921–1071 AD and 1821–1898 AD.