Paleoglacial records from Kavron Valley, NE Turkey: Field and cosmogenic exposure dating evidence
Introduction
Paleoglacial research on the last glacial cycle bound by the Last Interglacial and the Holocene depends directly on an understanding of the complexities of actual atmospheric circulation patterns and their variability. This simple observation holds especially true for Anatolia, which is situated in the Eastern Mediterranean Region between 36°–42°N and 26°–45°E. Anatolia is extremely sensitive to even minor changes in the influence of each system resulting in precipitation changes. As glaciers react sensitively to changes in temperature, moisture and radiation balance, their changes in mass balance provide a geological record and so constitute a direct geoarchive of climate change. Glacial deposits are located in the Black Sea, the Taurus and Eastern Anatolian Mountains, Uludağ and on isolated extinct volcanic cones in the interior, such as Mount Erciyes, Süphan and Ararat (Çiner, 2004; Akçar and Schlüchter, 2005 and references therein).
The Last Glacial Maximum (LGM) is the period, when the most recent glacial cycle was at its peak with maximum global ice volume during Marine Isotope Stage 2 (MIS2) (Martinson et al., 1987). This glaciation is extensively mapped and referred to as Wisconsinian, Weichselian or Wurmian, depending on the location of studies in North America, northern Europe or the Alps. Respectively, the first observations on the presence of glaciers and glacial deposits in the Eastern Black Sea Mountains were made in the 1840s, although scientific studies did not begin until the 20th century with their description and mapping. However, these early reports rely mostly on general observations and theoretical assumptions rather than on direct field data (Kayan, 1999; Akçar and Schlüchter, 2005 and references therein). Due to the lack of detailed mapping and dating in paleoglaciation studies in Turkey, the timing of the LGM still remains open there. The determination of the positions of the jet streams and jet maxima during glaciations (especially during the LGM) is crucial in order to understand the transport of moisture during cold periods in the Eastern Mediterranean Region. This can be done by identifying the amplitude and frequency of paleoglacier advances in Anatolia, and can be done by the mapping of geometry and the dating of prior ice bodies. This study has taken the Quaternary units of the Kavron Valley in the Eastern Black Sea Mountains (Fig. 1), mapping them in detail and using cosmogenic 10Be for the surface exposure dating of 22 granitic samples, (1) to produce the first dating of the Quaternary paleoglaciations from Turkey, (2) to establish the chronology of the Quaternary paleoglaciations and (3) to deduce implications on the Quaternary paleoclimate of Anatolia and on the paleo-atmospheric circulation patterns.
Section snippets
Present climate
Anatolia may be considered a link area between North Atlantic–Alpine–Western Mediterranean Cyclonic (Macklin et al., 2002) and Arabian–Indian–Tibetan Monsoon climate patterns, as the Anatolian Peninsula lies at the junction of three main atmospheric systems: (1) main middle to high-latitude westerlies to the north and northwest, (2) mid-latitude subtropical high-pressure systems that generally extend from the Atlantic across the Sahara and (3) monsoon climates of the Indian subcontinent and
Study area
The Kavron Valley is situated in the Kaçkar Mountain in the Eastern Black Sea Mountain range of northeastern Turkey (Fig. 1), lying approximately 40 km south of the coast. It is a north–south-oriented, typical U-shaped glacial valley approximately 12 km in length (Fig. 3). Kaçkar Mountain is the highest peak of the mountain range rising to 3932 m (a.s.l.), with the base of the Kavron Valley falling to approximately 1600 m, and consisting of a main and three tributary valleys. These three
Methodology
In this study, sampling strategies defined in Ivy-Ochs (1996), Tschudi (2000) and Akçar (2006) were followed. One sample from a tor, three samples from glacially abraded bedrock surfaces and 18 samples from granitic moraine boulders were collected. The geomorphic setting, lithology and size were carefully considered parameters when choosing samples that were believed to be the best available from a given locality. Within the granitic moraine boulders, especially the largest boulders with wide
Results
10Be concentrations, values for shielding correction and calculated cosmogenic exposure ages (Age-1, Age-2, Age-3 and Age-4) for 22 samples processed during this study, are presented in Table 2. All exposure ages include corrections for thickness, dip of the rock surface and shielding by surrounding topography. Age-1 is apparent age without any snow and erosion corrections. Age-2 presents snow corrected (no erosion correction) exposure age. Age-3 shows snow and erosion (2±0.5 mm kyr−1) corrected
Discussions
During the LGM, the winter position of the PFJ is assumed to be south the LGM coastline of the Black Sea. Such a southerly position of the PFJ should have resulted in a larger Siberian High Pressure System during winter, and colder and drier cP. So, the limited fetch area over the Black Sea and colder and drier weather conditions resulted in lower moisture take-up of these air masses. Lower moisture take-up would then have caused lower precipitation in the Eastern Black Sea Mountains. Although
Conclusions
With the new 22 10Be cosmogenic exposure ages, our study has revealed that the timing of the LGM was during MIS2 in the Eastern Black Sea Mountains. In the Kavron Valley, the advance of the paleoglacier began at least 26.0±1.2 kyr ago, and continued until 18.3±0.9 kyr. The paleoclimatic conditions that caused the LGM advance of Kavron paleoglacier may be explained by the equilibrium between main accumulation of snow during winter and lowered summer insolation, resulting in a limited build-up of
Acknowledgments
We would like to thank Associate Prof. Dr. İsmail Ömer Yılmaz at Middle East Technical University (METU) in Ankara for his helpful comments. We also thank Prof. Dr. Dirk van Husen and Dr. Anne Reuther for their helpful comments and suggestions. We are grateful to Sally Lowick at University of Bern for her kind help during the preparation of this paper. We are also grateful to the editors; Dr. Frank Preusser and Dr. Marcus Fiebig for their help and patience during the preparation and the
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