ALBERT

Description: A limnogeological reconnaissance study was carried out on Lake Iznik, located in the southeast of the Marmara region of Turkey, involving a seismic survey and collection of short sediment cores. This lake is located on the middle branch of the North Anatolian Fault Zone (NAFZ), a transform plate boundary between the Eurasian and Anatolian Plates. It is, therefore, tectonically active and offers an opportunity to investigate the interplay of sedimentary and seismo-tectonic processes, as well as climate change and human impact in the region. Short cores of the three sub-basins, maximum length of 35.5 cm, recovered non-laminated, blackish clays and silts with varying amounts of biogenic and minerogenic (allochthonous, autochthonous) material, which documented almost the last 80 years of deposition and environmental history. High sedimentation rates in the deeper core sections are accompanied by changes in land use (conversion of woodland to farmland) in the northern areas of Lake Iznik, which caused the deposition of more weathered material (high K/Na ratios) and higher contents of Mn in the lake. A tendency towards eutrophic conditions within the last 20 years is indicated by high nutrient content (N, TOC, P), decreasing C/N-ratios, and characteristic diatom and cladoceran associations. Also increased pollution is revealed by higher Pb, Cu, and Zn contents and increased supply of human and animal faeces (high coprostanol content) during the last two decades. But simultaneous lower sedimentation rates towards the core tops complicate the reconstruction of recent and past eutrophication and pollution states of Lake Iznik. This requires an extension of the pilot study and deeper sediment cores, to recover non-anthropogenic influenced sediment levels.

Description: New sediment cores were recovered from two sites in the central part of Lake Iznik with the overall aim of reconstructing past environmental conditions of the Marmara region. The composite profile presented here, IZN09/LC2&LC3, encompasses the late Pleistocene to Holocene transition (c. 36 ka cal BP) which is the longest lacustrine record in this region obtained to date. A lithostratigraphical and geochronological framework builds the basis to establish a composite section for first inferences on the paleo Lake Iznik. The recovered sedimentary record was divided into five stratigraphic units which can be correlated between the different coring locations. The proposed age-depth model is based on eleven 14C dates (eight radiocarbon-dated levels) and two tephra layers, supported by three OSL ages. The modeled age distribution of the Ca/Ti ratio and magnetic susceptibility express variations in the carbonate accumulation in balance with clastic sediment input. Starting from the end of MIS 3 with high clastic input, Lake Iznik passed through a low lake-level during the Last Glacial Maximum (LGM), delineated by a sublitoral sedimentary facies, and reduced sedimentation rates. After c. 18 ka cal BP, the onset of primary carbonate deposition might be linked to meltwater inflow into the lake as well as onset of lake productivity. From this time onward, there is a gradual increase in carbonate accumulation punctuated by the occurrence of an iron-sulfidic layer which coincides with the Younger Dryas event. At the early Holocene, the lake presents a minimum level as reflected by the maximum carbonate production, followed by a lake level rise at c. 9 ka cal BP which reached a level similar to the modern situation.