Cold and wet Last Glacial Maximum on Mount Sandıras, SW Turkey, inferred from cosmogenic dating and glacier modeling
Introduction
The evidence of past glacial activities in mountain settings provides direct information of the magnitude and frequency of past climate changes. Because of the unique location of Turkey in the transition zone between the temperate Mediterranean climates influenced by North Atlantic cyclones (Macklin et al., 2002) and the subtropical high pressure climatic zone (la Fontaine et al., 1990), the paleoclimate of Turkey is highly sensitive to climatic perturbations that affect the position and/or intensity of the westerly storm tracks that carry moisture from the North Atlantic and Mediterranean Sea. Thus, studying the timing and extent of past glacial activity as a proxy of past climates on Turkey can reveal valuable information on Late Quaternary climate changes.
Several mountain ranges in Turkey supported glaciers during the Late Quaternary (Erinç, 1952; Messerli, 1967; Birman, 1968; Kurter and Sungur, 1980; Çiner, 2004; Akçar et al., 2007). Among these, the Taurus Mountain Range, in south Anatolia, has two-thirds of the previously glaciated mountains in the country. On the far east (Fig. 1), Mount Cilo (4135 m) has the largest glaciated area in Turkey, including ice caps and valley glaciers up to 4 km long (Kurter, 1991). In the central Taurus, Mount Aladağlar (3756 m) has a well-preserved moraine record of extensive Early Holocene glaciers (Klimchouk et al., 2006; Zreda et al., 2006). While much lower than their eastern counterparts, the western Taurides also have several mountains with evidence of Pleistocene glaciers. Mount Dedegöl (2990 m, Zahno et al., 2007), Beydağ (3086 m, Messerli, 1967), Akdağ (3016 m, Onde, 1952) and Sandıras (2295 m, de Planhol, 1953; Doğu, 1993) (Fig. 1) show several cirques and well-preserved glacier related landforms especially on their north and northeast facing slopes. Today, due to the increasing effect of continentality from west to east in Anatolia, western mountains experience wetter and warmer climate than the eastern mountains. Today, active glaciers are present only in central and eastern mountains, and their sizes are increasing from west to east. Additionally, Late Pleistocene equilibrium line altitude (ELA) estimates in Turkey support this continental effect (Messerli, 1967; Erinç, 1971, Erinç, 1978; Atalay, 1987). During the Last Glacial Maximum (LGM, 21,000 calendar years ago), western Anatolian mountains had ELAs as low as 2000–2400 m while eastern mountains had ELAs about 3000–3200 m.
Glacial deposits in all these mountains have been studied to some degree, but few of them have been dated numerically. Most of the age estimates for glacial deposits are based on relative dating techniques, including stratigraphic relationships, degree of weathering and soil development (de Planhol, 1953; Birman, 1968; Doğu, 1993). Generally, previous studies assigned Late Pleistocene to the age of glaciation in the southwest Taurus Mountains (de Planhol, 1953; Doğu, 1993; Çiner, 2004 and references therein).
The glacial landforms on Mount Sandıras were mapped and their lithostratigraphy described in detail by de Planhol (1953) and Doğu (1993). However, because these glacial deposits have not been dated numerically, the exact timing of glaciations is unknown, which precludes paleoclimatic interpretation based on the glacial records. In this study, we examined the timing (from the age of landforms) and magnitude (from the position of ice margins) of paleoclimatic changes on Mount Sandıras by using the cosmogenic 36Cl exposure dating method. We modeled the glacier response to climatic changes using a glacier model to reconstruct temperature and precipitation at the time of glaciation. Finally, we compared our paleoclimatic findings with other Late Quaternary climate proxies from the Eastern Mediterranean region.
Section snippets
Physical setting and climate
Mount Sandıras (37.1°N, 28.8°E, 2295 m above mean sea level), also known as Çiçekbaba (Flower father, in Turkish), Sandras or Gölgeli Dağları (Shaded Mountains), is the southwestern most previously glaciated mountain in the Anatolian Peninsula (Fig. 1). The mountain is located about 40 km from the Mediterranean coast. The land elevation increases rapidly towards inland creating a natural climatic barrier between the coastal area and the interior.
The summit of Mount Sandıras is a plateau
Evidence of glacial action on Mount Sandıras
Philippson (1915), cited by Doğu (1993), first described evidence of former glaciations on Mount Sandıras. de Planhol (1953) suggested that an ice cap covered the flat top of the mountain during the Würm glacial age and the tongues of that ice cap reached an altitude of 1900 m on the north side. He calculated the Würm glaciation snow line (similar to ELA) to be at 2000–2050 m and proposed that this snow line lower than that on other mountains in southwestern Turkey is due to the tectonic lowering
Determination of 36Cl ages
We used the cosmogenic 36Cl method (Davis and Schaeffer, 1955; Phillips et al., 1986; Zreda and Phillips, 2000) to determine surface exposure ages of boulders from moraines associated with the Sandıras glaciation. Chlorine 36 is produced in rocks by collisions of cosmic-ray neutrons and muons with atoms of Cl, Ca and K (Zreda et al., 1991). Once produced, it remains in place and accumulates continuously with time (Zreda and Phillips, 2000). Because the production rates of 36Cl from the three
Cosmogenic 36Cl exposure ages
We dated six boulders from the Kartal Lake Valley and three from the Northwest Valley (Fig. 2; Table 1). All boulder ages include correction for thickness and shielding by surrounding topography and snow. The uncertainties quoted for the boulder ages were calculated by propagation of analytical errors on 36Cl/Cl and on Cl (both reported by the AMS laboratory) and assuming a 20% uncertainty on the calculated nucleogenic component. Boulder age uncertainties are based only on analytical errors and
Conclusion
The most extensive glacial advance on Mount Sandıras ended by 20.4±1.3 ka ago, and the final deglaciation commenced by 16.2±0.5 ka ago. Modeling of glacier mass balance shows a wide range of possible temperatures and precipitation rates necessary to produce Mount Sandıras glaciers. Without independent estimates of temperature and precipitation for LGM, model results do not provide a unique combination of these variables based on simulated ice extent. An LGM half as wet as today requires a cooling
Acknowledgments
This research was supported by the US National Science Foundation (Grant 0115298) and by the Scientific and Technological Research Council of Turkey (TÜBİTAK) (Grant 101Y002).
References (88)
- et al.
Paleoglacial records from Kavron Valley, NE Turkey: field and cosmogenic exposure dating evidence
Quaternary International
(2007) - et al.
An ion-selective electrode method for determination of chlorine in geological materials
Talanta
(1983) - et al.
Late Quaternary paleoclimate in the Eastern Mediterranean region from stable isotope analysis of speleothems at Soreq Cave, Israel
Quaternary Research
(1997) - et al.
Sea-land oxygen isotopic relationships from planktonic foraminifera and speleothems in the Eastern Mediterranean region and their implications for paleorainfall during interglacial intervals
Geochimica et Cosmochimica Acta
(2003) Turkish glaciers and glacial deposits
- et al.
Spatial and temporal distribution of secondary cosmic-ray nucleon intensities and applications to in situ cosmogenic dating
Earth and Planetary Science Letters
(2003) - et al.
Extended scaling factors for in situ cosmogenic nuclides: new measurements at low latitude
Earth and Planetary Science Letters
(2006) - et al.
Determination of cosmogenic 36Cl in rocks by isotope dilution: innovations, validation and error propagation
Chemical Geology
(2006) - et al.
Temperature and salinity variations of Mediterranean Sea surface waters over the last 16 000 years from records of planktonic stable oxygen isotopes and alkenone unsaturation ratios
Palaeogeography Palaeoclimatology Palaeoecology
(2000) - et al.
Terrestrial in-situ cosmogenic nuclides: theory and application
Quaternary Science Reviews
(2001)