Middle-to-Late Holocene Climate Change in Lagoon Lake Mert (NW Black Sea) and Its Hydrological Connection with the Black Sea: evidences from multi-proxy records

Coastal areas and related sedimentary environments are remarkable providers of valuable information about climatic changes and sea level oscillations. Lake Mert was formed as a shallow Black Sea coastal lagoon that contains various mixtures of marine and freshwater sources. This study presents sedimentological, geochemical and paleontological analyses of five sediment cores recovered from the lake which has been severely influenced by sea level change and local climate over the last 6.5 cal. ka BP. The environmental and climatic records obtained by multi-proxy analyses of the cores (µ-XRF, total organic carbon, stable isotope, pollen analysis and foram content) that are confidently correlated with other regional and global climate signals. In addition, Lake Mert also remains a challenge to identify and quantify dynamic changes in time on the coastal plain, thus, it possibly reflects hydrologic changes in the Black Sea since the middle Holocene. Analysis of lithology together with paleontological content of the studied cores reveal three main depositional units, each of them indicates varying areal facies distribution due to highly dynamic depositional settings in lake. Accordingly, the main lithofacies in the cores from bottom to top are defined as a relict lacustrine sediment older than 6.5 cal. ka BP (Unit 3), coastal and deltaic facies deposited between 6.5 to 4.5 cal. ka BP (Unit 2) and the younger lagoon-marine sediment (Unit 1).

Moreover, the correlation of well-dated sedimentological and geochemical proxies with the sea level and sea surface salinity records from the Black Sea allows us differentiate various phases of hydrologic changes due to connections with the Lake Mert during the middle-to-late Holocene. Our preliminary results suggest that the relict Mert Lake was first invaded by the Black Sea waters prior to 6.5 cal. ka BP, and then remained its fully connection until ~5.3 cal. ka BP due to subsequent inflow of the Mediterranean Sea via Bosporus. Furthermore, the decelerated sea level rise between 5.3 and 4.5 cal. ka BP gave rise to return semi-closed lagoon phase, restricting mixture with the Black Sea waters as inferred from stable oxygen isotope record. The later period, particularly after 3.5 cal. ka BP, was associated with more Euryhaline condition in the lake based on the paleontological content of the core sediment. The local climate changes are recorded in Lake Mert as a wet period between 6.5 and 4.5 cal. ka BP, a dry period between 4.5 and 2.9 cal. ka BP and wetter period after 2.9 cal. ka BP, respectively.