‘PALEOVAN’, International Continental Scientific Drilling Program (ICDP): site survey results and perspectives

Abstract

Lake Van is the fourth largest terminal lake in the world (volume 607 km³, area 3570 km², maximum depth 460 m), extending for 130 km WSW–ENE on the Eastern Anatolian High Plateau, Turkey. The sedimentary record of Lake Van, partly laminated, has the potential to obtain a long and continuous continental sequence that covers several glacial–interglacial cycles (ca 500 kyr). Therefore, Lake Van is a key site within the International Continental Scientific Drilling Program (ICDP) for the investigation of the Quaternary climate evolution in the Near East (‘PALEOVAN’). As preparation for an ICDP drilling campaign, a site survey was carried out during the past years. We collected 50 seismic profiles with a total length of ∼850 km to identify continuous undisturbed sedimentary sequences for potential ICDP locations. Based on the seismic results, we cored 10 different locations to water depths of up to 420 m. Multidisciplinary scientific work at positions of a proposed ICDP drill site included measurements of magnetic susceptibility, physical properties, stable isotopes, XRF scans, and pollen and spores. This core extends back to the Last Glacial Maximum (LGM), a more extended record than all the other Lake Van cores obtained to date. Both coring and seismic data do not show any indication that the deepest part of the lake (Tatvan Basin, Ahlat Ridge) was dry or almost dry during past times. These results show potential for obtaining a continuous undisturbed, long continental palaeoclimate record. In addition, this paper discusses the potential of ‘PALEOVAN’ to establish new results on the dynamics of lake level fluctuations, noble gas concentration in pore water of the lake sediment, history of volcanism and volcanic activities based on tephrostratigraphy, and paleoseismic and earthquake activities.

Introduction

Lake Van is situated on a high plateau in eastern Anatolia, Turkey. Extending for 130 km WSW–ENE, it is the fourth largest terminal lake in the world by volume (volume 607 km³, area 3570 km², maximum depth 460 m). It is in a region where the Afro/Arabian Plate from the south meets the Eurasian Plate from the north and east (Fig. 1). The lake fills a tectonic depression within an active fault system that causes regional volcanism, earthquakes and hydrothermal activity (Degens and Kurtman, 1978; Kipfer et al., 1994, Keskin, 2003, Şengör et al., 2003). Two semi-active volcanoes rise in the immediate vicinity of the lake (1674 m a.s.l.) at Nemrut Dagi (3050 m a.s.l.) and Süphan Dagi (3800 m a.s.l.) (Karaoglu et al., 2005). Evaporation processes, hydrothermal activities and chemical weathering of volcanic rocks create extreme alkalinity of the lake water (alkalinity 155 m eql⁻¹, pH 9.81, salinity 21.4‰; Kempe et al., 1991) and make Lake Van the greatest soda-water lake in the world (Kadioglu et al., 1997).

Subaerial terraces and sedimentological evidence demonstrate that lake level changes of up to several hundred meters occurred during the last 20 kyr. This indicates that the lake reacts sensitively to alteration of the hydrological regime in response to climate change (Landmann et al., 1996a). The lake basin is near a tectonic plate triple junction that allows fluids from the Earth's mantle to accumulate in Lake Van and the nearby crater lake of Nemrut volcano (Kipfer et al., 1994).

The sediments of Lake Van are annually laminated for nearly 14 kyr (Kempe and Degens, 1978, Lemcke, 1996, Landmann et al., 1996b, Wick et al., 2003), which is ideal for creating high-resolution climate, tectonic and volcanic histories. The lake's position at the junction of the atmospheric south-western jet stream and northern branch of the Subtropical High makes it climatically sensitive (Fig. 2). The jet stream steers the cyclone tracks that are responsible for supplying moisture from Mediterranean air masses during winter. The location of the Subtropical High controls the southward extension of the dry continental air masses of north-eastern Europe and Asia (La Fontaine et al., 1990, Akcar and Schlüchter, 2005).

Within the sensitive climate region of north-eastern Anatolia, the Lake Van record represents an excellent continental climate archive between the Black Sea, the Arabian Sea and the Red Sea (e.g. Roberts and Wright, 1993, Cullen and de Menocal, 2000, Lamy et al., 2006). The ICDP PALEOVAN project creates the potential for a precise correlation of a continental lacustrine record with other environmental archives, such as ice-cores, marine sediments and speleothems (Bar-Matthews et al., 2003, Fleitmann et al., 2003, NGRIP members, 2004). The combination of climatic sensitivity and a varved sediment lithology makes Lake Van a suitable candidate to disentangle and isolate processes and patterns of climate and environment. The lake's size and depth suggest that the lake may have deep sedimentary deposits spanning multiple glacial–interglacial cycles (Degens and Kurtman, 1978). The ‘PALEOVAN’ project could thus provide climatic and environmental data for eastern Anatolia and the Near East region of unprecedented duration and quality, making Lake Van a key site not only for ICDP (International Continental Scientific Drilling Program) (Harms et al., 2007, Litt et al., 2007), but also for other international geoscience programs such as PAGES (Past Global Changes) (Battarbee et al., 2004).

In the past few years, geological and geophysical site surveys were done in preparation for the PALEOVAN ICDP drilling campaign. The main aim of this paper is to summarize the most important results of these surveys and to analyze the depositional regimes of Lake Van, characterize the Holocene and last glacial sediments, and evaluate the potential of Lake Van for long continuous sedimentary records.