Climate change during the last 200,000 years at the Lake Van area (Turkey)

The climate variability during the Quaternary represents the closest analogy to present-day climate change. Lake Van (Anatolia, Turkey) promises to be an excellent palaeoclimate archive because it has the potential to yield long continental records covering several glacial-interglacial cycles from annually laminated sediments, hence making the lake a key site for the investigation of the Quaternary climate evolution in the Near East. Our investigations will be part of the International Continental Scientific Drilling Program (ICDP) PaleoVan, including palynology, sedimentology, magnetostratigraphy, geochemistry, varve counting, and radiometric dating, on drill core samples, expected to comprise the last 600,000 years ( 220 m core profile). The investigations will focus on sediment intervals from pollen zones reflecting glacial-interglacial transitions. The primary goal of the proposed project is to provide evidence about the applicability of biomarker and stable isotope data (C, H) as proxies for ecological and climatic changes during the Quaternary. Based on the results of well-logging, XRF-scans, and palynological screening, the following potential proxies will be evaluated for their relations with paleoclimatic changes in terrestrial environments: Biomarkers as proxies for floral changes: A significant contribution to the present knowledge about the chemotaxonomical value of biomarkers is expected by combining organic geochemical with palynological and paleobotanical data from lake sediments and macrofossils during the proposed study. The results will contribute to the reconstruction of floral assemblages and vegetational changes in sedimentary sequences with poor preservation of palynomorphs. Carbon isotope data of land plant material as proxies for carbon cycling: Carbon isotopic composition of land plant remains and land plant-specific biomarkers will be used to track changes in the ancient carbon cycle and isotopic composition of atmospheric CO2. The results will be related to changes in vegetation and climate, based on palynological results and geochemical proxy data. Warming events are expected to be synchronous to changes in 13C of atmospheric CO2 coupled to pCO2 variations. Hydrogen isotope data of individual biomarkers as proxies for hydrological changes: The planned analyses of D/H ratios of long-chain n-alkanes and alkenones, will be used to reconstruct changes in the hydrogen isotopic composition of environmental water at Lake Van during the Quaternary. The combination of palynology and geochemical temperature proxies with D variations of land plant biomarkers are expected to enable the distinction of changes in humidity versus air temperature, often not possible from paleobotanical data alone. The integration of the data into a synthesis study, will allow new insights into the response of vegetation to past rapid climate change. Abrupt climate changes are suggested to lead to extreme events like droughts, floods, severe storms and others, observed today. An understanding of the intensity and frequency of these abrupt changes in the past and their effect on vegetation might enable us to prepare for future climate change by improved resource management and other policy issues.

The main goals of the project were to obtain information about climatic changes during the last 250,000 years (temperature, humidity) in Eastern Anatolia and their influences on aquatic communities and vegetation, based on geochemical analyses on sediment cores from Lake Van (Turkey). Within the frame of the project, sediments covering the last glaciation (MIS-2) to Holocene (0 30,000 years B.P.), Dansgaard-Oescher (DO) interstadials (MIS-3; 42,000 55,000 years B.P.), and during MIS-7 to MIS-6 (130,000 250,000 years B.P.) have been investigated. These periods are characterized by an existing excellent age model. Generally, warmer periods show higher contents of organic carbon (TOC), enhanced reflectivity (reflectance B*), and increased abundances of oak and pine pollens. Increased bioproductivity in the lake and in vegetation density in the catchment area after warming events are indicated by higher TOC-normalised concentrations of long-chain alkenones and sterols (characteristic for algae, diatoms, zooplankton, dinoflagellates, etc.), and long-chain n-alkanes (characteristic for land plants). A main target was the development of an analytical procedure for the seperation of alkenones for their hydrogen isotope analyses. The established method enables the analysis of D on individual alkenones. Based on concentration ratios of branched tetraether lipids (GDGTs) and the application of established transfer functions, relative differences in mean annual air temperatures of 2-3C during DO interstadials, and of 3-5C during the transition from last glaciation (MIS-2) to the Holocene are revealed. Hydrogen isotopic composition of long-chain n-alkanes suggest enhanced precipitation (humid conditions) during interstadials and interglacials. Cold periods are characterized by increased evapotranspiration rates, indicating arid conditions. Estimates about the magnitudes of changes in precipitation amounts (200 350 mm per year) are in good agreement with information about lake level changes and with the results from coupled atmospheric-ocean-ice-vegetation model simulations (LOVECLIM).