f A Climate Record of the Last 1400 yrs from the Lake Çubuk (Göynük, Bolu, NW Anatolia) Based on Multi-Proxy Investigations

A paleoclimatic study was carried out in the Lake Çubuk, 15 km to the east of Göynük town (Bolu, NW Anatolia). 3 m-thick core has been taken from the lake bottom and a trench has been opened at the lake margin. The core and trench samples were analyzed according to lithologic, stable isotope, geochemistry, pollen, ostracod and diatom components. Lithologically, the core consists of gray to green muds in the first 50 cm interval from the top. Alternation of fine sandy intervals and gray muds take place between 50-150 cm and dominantly greenish gray mudstones lie between 150-300 cm. Lamination and organic rich levels are almost absent through the core. According to the age model based on three 14C analysis, the base of the core goes back to 1400 yr BP. The sand rich interval was deposited within a very short time span (50 yrs) just after 1400 AD. Stable δ18O isotope data shows a general negative shift indicating a decrease in precipitation after 1450 AD. Certain geochemical proxies indicate the increase of biological productivity as well as oxidation in the lake water. Ratio of total tree and pinus pollens decreased significantly while shrub pollens considerably increased. Conformably, benthic/planktic diatom ratio slightly increases. The sandy event interval mentioned above is characterized by unique occurrence of certain diatom specious such as autocoseria sp. In the lower part of the core spanning between 1400 - 500 AD, isotopic proxies display two cold and dry periods peaked at 850 AD and 1250 AD respectively. During these century-lasting climate events stable isotopes (δ13C, δ18O) shift to more negative values, geochemical proxies for biological productivity and detrital input considerably decrease. These cold events are also characterized by enriched ostracod fauna and higher benthic/planktic diatom ratio indicative of lower lake levels. The Lake Çubuk climate record that comprises the global Little Ice Age and Medieval Warm Period was also compared with the previous regional/global patterns and discrepancies are discussed.