Natural and human-induced environmental change in southern Albania for the last 300 years - Constraints from the Lake Butrint sedimentary record

A sediment core from Lake Butrint in southwestern Albania contains an annually-layered sequence coveringthe last ∼300 years. It provides thus an exceptionally well-dated time series to study past climate-drivenenvironmental changes, as well as anthropogenic perturbations along the coast of the Ionian Sea. The varvesare composed of organic-rich carbonate couplets and detritus-dominated clay layers. The first are depositedduring spring-to-fall, and reflect the chemistry of the lake, which, in turn, is sensitive to 1) the relativeimportance of marine versus freshwater inputs, 2) relative evaporation rates, and 3) the productivity cyclewithin the lake. The detrital laminae are deposited during winter, reflecting precipitation and runoffconditions during the wet season. A 2–3‰ stable carbon isotope ratio shift in both bulk organics andauthigenic carbonates was attributed to increasing eutrophication towards the end of the 20th century, andvalidated by historical and instrumental data. An increase in the δ18O of authigenic carbonates by more than8‰ indicates the progressive salinization of the lake, which can primarily be attributed to man-madeperturbations that reduced the freshwater input to the lake and/or enhanced the exchange with seawaterfrom the nearby Ionian Sea. A recent increase in the relative evaporation versus precipitation rates may haveadditionally contributed to the observed 18O enrichment in the Lake Butrint carbonates. The interdecadalcyclicity in the thickness of the detrital laminae seems to be at least partially controlled by NAO and/orENSO-like phenomena that modulate precipitation patterns in the eastern Mediterranean. Thus, this studydemonstrates the potential of combining microstratigraphic and stable isotopic tools to disentangleanthropogenic and natural environmental changes in Lake Butrint, validated by historical records.