Surface exposure dating reveals MIS-3 glacial maximum in the Khangai Mountains of Mongolia

Quaternary Research 82 (2014) 297–308

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Surface exposure dating reveals MIS-3 glacial maximum in the Khangai Mountains of Mongolia Henrik Rother a,⁎, Frank Lehmkuhl b, David Fink c, Veit Nottebaum b a b c

Institute for Geography and Geology, University of Greifswald, F.-L-Jahnstr. 17a, 17489 Greifswald, Germany Department of Geography, RWTH Aachen University, Wüllnerstr. 5b, 52056 Aachen, Germany Institute for Environmental Research, Australian Nuclear Science and Technology Organisation (ANSTO), PMB1, Menai 2234, Australia

a r t i c l e

i n f o

Article history: Received 2 July 2013 Available online 14 July 2014 Keywords: Late Pleistocene glaciations Mongolia Khangai Mountains 10 Be exposure dating Glacial chronology

a b s t r a c t This study presents results from geomorphological mapping and cosmogenic radionuclide dating (10Be) of moraine sequences at Otgon Tenger (3905 m), the highest peak in the Khangai Mountains (central Mongolia). Our findings indicate that glaciers reached their last maximum extent between 40 and 35 ka during Marine Oxygen Isotope Stage (MIS) 3. Large ice advances also occurred during MIS-2 (at ~23 and 17–16 ka), but these advances did not exceed the limits reached during MIS-3. The results indicate that climatic conditions during MIS-3, characterized by a cool-wet climate with a greater-than-today input from winter precipitation, generated the most favorable setting for glaciation in the study region. Yet, glacial accumulation also responded positively to the far colder and drier conditions of MIS-2, and again during the last glacial–interglacial transition when precipitation levels increased. Viewed in context of other Pleistocene glacial records from High Asia, the pattern of glaciation in central Mongolia shares some features with records from southern Central Asia and NE-Tibet (i.e. ice maxima during interstadial wet phases), while other features of the Mongolian record (i.e. major ice expansion during the MIS-2 insolation minimum) are more in tune with glacier responses known from Siberia and western Central Asia. © 2014 University of Washington. Published by Elsevier Inc. All rights reserved.

Introduction Situated at the northern fringe of the mountainous interior of Central Asia, the Khangai Mountains (46°–48°N/96°–103°E) represent one of the most landlocked high mountain systems in the world (Fig. 1). Climatically, the wider region is influenced by several major atmospheric systems, comprising chiefly the Siberian–Mongolian anticyclone and the mid-latitude Westerlies. During the late Quaternary, changes in the interplay between these systems caused substantial climatic variability, with drastic effects on hydrological conditions (e.g., An et al., 2012; Feng et al., 1998; Kurita et al., 2003; Lehmkuhl and Haselein, 2000; Sun et al., 2009; Yang et al., 2004). The environmental impact of these variations was particularly severe as the region is located within the ecologically sensitive transition zone between the Central Asian deserts to the south and the Siberian steppe and forest areas to the north. Since the late 1990s, a range of new geological archives documenting the late Quaternary climatic evolution of the Mongolian region have become available. These include records of endorheic lake

⁎ Corresponding author. E-mail address: [email protected] (H. Rother).

http://dx.doi.org/10.1016/j.yqres.2014.04.006 0033-5894/© 2014 University of Washington. Published by Elsevier Inc. All rights reserved.

level fluctuations (Grunert et al., 2000; Harrison et al., 1996; Komatsu et al., 2001; Watanabe et al., 2009), fluvial–alluvial dynamics (Lehmkuhl and Haselein, 2000; Owen et al., 1997), aeolian dust deposition (Lehmkuhl, 1997; Yang et al., 2004), changing vegetation patterns (Schlütz et al., 2008; Tarasov et al., 1999) and variations in permafrost extent (Owen et al., 1998). Taken together, these records suggest an overall trend of increasing aridity in Mongolia and NW-China over the past 100 ka. However, there is also evidence that this development was interrupted by several phases of enhanced humidity, most prominently during Marine Oxygen Isotope Stage (MIS) 3, the last glacial transition and the early-mid Holocene period (Grunert et al., 2000; Murakami et al., 2010; Pachur et al., 1995; Yang et al., 2004). The coldest phase during the last glacial cycle is associated with MIS-2 and coincided with extremely arid conditions leading to marked low stands of lakes in the ‘Valley of Great Lakes’ and the development of extensive dune fields (Grunert et al., 2000; Hülle et al., 2010). So far, relatively few late Quaternary mountain glacier records from Mongolia have been analyzed, but large Pleistocene glaciations have been confirmed in at least five mountain systems: the Mongolian Altai, the Khangai, and somewhat smaller, in the Khenty Mountains (NE of Ulaanbaatar), the Darhad area (N-Mongolia) and the Gobi Altai (e.g., Gillespie et al., 2008; Lehmkuhl, 1998; Lehmkuhl et al., 2004, 2011). At present, significant glaciation survives only in the Mongolian

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H. Rother et al. / Quaternary Research 82 (2014) 297–308

Figure 1. Overview map of central and western Mongolia. Shown are the geographic positions of the Mongol and Gobi Altai, the ‘Valley of Great Lakes’ and the Khangai Mountains, with the location of the Otgon Tenger study site approximately 700 km W of the capital Ulaanbaatar.

Altai, covering an area of c. 850 km2 (Klinge, 2001), while glaciation in the Khangai Mountains is limited to a single small ice field (at Otgon Tenger). By contrast, the total glaciated area during the late Pleistocene is estimated to have covered an area of about 30,000 km2 in the Mongolian Altai (Klinge, 2001) and approximately 13,000 km2 in the Khangai Mountains (Florensov and Korzhnev, 1982). Based on the pioneering work by Russian scientists, the stratigraphic division of Mongolia's Pleistocene has traditionally followed the Siberian stratigraphy and nomenclature. According to Florensov and Korzhnev (1982) and Arkhipov et al. (1986) the region's last glacial cycle (‘Zyrianka Glaciation’) is divided into two glacial phases named Early Zyrianka glaciation and Sartan glaciation, which are separated by the Kargynski interstade. Based on relative weathering characteristics (e.g., clast weathering rinds, degree of moraine degradation, thickness of soil development) and on the mapping of separate moraine-outwash systems, two to three major ice advances have been recognized and correlated to the Early Zyrianka and Sartan glaciations (Lehmkuhl, 1998; Lehmkuhl et al., 2004, 2011). In recent years, Gillespie et al. (2008), working in the Darhad Basin, have presented the first set of moraine surface exposure dates from Mongolia. Their results indicate a large ice advance between 19 and 17 ka (MIS-2) and possibly between 53 and 35 ka (MIS-3), during the Kargynski interstade. No direct dating of glacial moraines in the Khangai Mountains has yet been undertaken. Indirect evidence for an ice

advance, contemporaneous with the global Last Glacial Maximum (LGM), comes from a luminescence age of 21.7 ka (Lehmkuhl and Lang, 2001) obtained from aeolian deposits above glaciofluvial gravels in the Baydragiyn Gol (for location see Fig. 1). Although these findings represent important progress, there remains a significant lack of ‘absolute’ dating to constrain glacial timings in this region. As a consequence, the overall picture regarding the chronology and climatic forcing mechanisms of past glaciations in Mongolia remains tentative, until more robust age control becomes available. The context for this task is provided by an increasing number of numerical dating studies reconstructing late Quaternary glacial histories in other mountain systems of Central and High Asia1. Results indicate that glacial timings differed significantly across this vast region: glaciers in the western and north-western parts of High Asia (i.e. Pamir and TienShan) reached their maximum extent early during the last glacial cycle (i.e. MIS 5 and 4) broadly contemporaneous with climatic cold phases recorded in the Northern Hemisphere (Abramowski et al., 2006; Koppes et al., 2008; Owen et al., 2012; Röhringer et al., 2012; Zech, 2012). Glacier systems within the monsoon influenced regions of Tibet, the Himalaya and the Hindu Kush, in contrast, exhibited glacial maxima during MIS-3 and a very restricted ice extent during MIS-2 1 ‘High Asia’ is defined here as the mountainous interior of Asia, comprising the high mountain systems of the Tibetan Plateau and its surrounding areas.

H. Rother et al. / Quaternary Research 82 (2014) 297–308

(Heyman et al., 2011a; Kamp and Haserodt, 2004; Owen et al., 2008). For these regions it has been suggested that changes in glacial volume were primarily driven by variations of monsoonal and westerly precipitation (Lehmkuhl and Owen, 2005; Owen et al., 2008), highlighting the potential value of these records for reconstructing past atmospheric dynamics. As described above, the absolute chronology of major glacial events is poorly resolved for Mongolia and most intra- and inter-continental correlations of glacial signals from this region remain controversial. Specifically, it is still unclear whether Mongolia's late Pleistocene ice maxima coincided with insolation minima (early or late during the last glacial cycle), or, alternatively, whether glacial maxima occurred during phases of less severe cooling but increased moisture supply. To address these questions, we present mapping results and a set of cosmogenic exposure ages from a well preserved glacial sequence in the western Khangai Mountains. In this study, we aim to (1) establish extent and numerical chronology of major late Pleistocene glacial fluctuations in central Mongolia, (2) correlate the timing of ice advances with paleoclimatological/paleoecological information available from other proxy records, and (3) assess the Mongolian data within the context of glacial records from other mountain belts across High Asia. Study area The Khangai Mountains are located in central Mongolia at the northwestern fringe of the Gobi Desert, and extend for roughly 650 km in a NW–SE direction covering an area of nearly 200,000 km2. Geologically, the range consists predominantly of Paleozoic clastic sedimentary rocks, which were deformed and weakly metamorphosed during a major late Paleozoic orogenic event (Zorin, 1999). Intrusions of plutonic complexes during the Permian and Jurassic produced several large granitic domes, which form the highest summits of the present-day relief. In many cases the Paleozoic and Mesozoic formations are cut by an erosion surface, representing a remnant of an extensive peneplain

299

that formed during the Cretaceous–Paleogene transition (Devyatkin, 1975). After a period of relative tectonic stability renewed uplift during the late Cenozoic triggered the extrusion of Tertiary basaltic rocks and the topographic doming of the old peneplain to altitudes between 3000 and 4000 m asl (Cunningham, 2001). Today, the crest of the Khangai Mountains forms a major watershed boundary separating the large intra-continental endorheic basins to the south from the Arctic Ocean drainage basin to the north. During the late Quaternary, the Khangai Mountains experienced extensive glaciation with major ice build-up concentrated in several high-altitude massifs (Fig. 2). Present glacial equilibrium line altitudes (ELAs) lie between 3750 and 3900 m asl effectively restricting the modern glaciation to the single highest peak of the range. During the late Pleistocene, ELAs were depressed by 750–1000 m (Lehmkuhl et al., 2011) and valley glaciers up to 30–40 km in length developed in many valleys. For the present study we selected the Otgon Tenger massif located in the extreme western portion of the Khangai range. This work is part of an ongoing study covering multiple glacial locations in the Altai and Khangai Mountains to reconstruct the signature of late Quaternary glaciations across the region. In addition to logistical considerations (relative ease of access), the study site was chosen because Otgon Tenger (3905 m asl) is the only peak in the Khangai Mountains that is currently glaciated. The area is characterized by broad summits and large cirques with numerous U-shaped valleys radiating from the central massif. Glacial landforms in the area are widespread and include terminal and lateral moraines, kame terraces, truncated spurs, hanging valleys, ice-overran bedrock features, glacial trimlines and abundant glacially transported boulders. Ice marginal landforms in the area consist primarily of latero-frontal dump moraines arranged in a lobate outline, and hummocky terrain which formed during the disintegration of heavily debris-mantled glacier lobes. Impressive sets of vertically stacked lateral moraines, extending up to 200 m above the valley floor, block off the lower portions of several tributary valleys in which lakes, such as Saran Nuur and Khokh Nuur, formed (Fig. 3).

Figure 2. Estimated maximum extent of the late Pleistocene glaciation in the Khangai Mountains after Florensov and Korzhnev (1982) and Lehmkuhl et al. (2004). For aerial context of depicted area see inset frame in Fig. 1. The distribution of the maximum ice limits indicates that during the local-LGM, glaciation was concentrated in five or six separate ‘glaciation centers’, each supporting extensive networks of interconnected valley glaciers (transection glaciers), plateau glaciers and small ice fields.

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Figure 3. Glaciers and glacial landforms in the study area: the image in (A) shows the current extent of glaciation on Otgon Tenger peak (August 2012), representing the only present glacier in the Khangai Mountains. The photos in (B) and (D) depict stacked and individual lateral moraines associated with the extended late Pleistocene ice positions located ca. 30 km from the headwaters. Image (C) shows a set of lobate terminal moraines preserved on the valley floor near Shuvuun Hill. Six glacial boulders from the moraine complex in (C) and three boulders from the lateral moraine in (D) were sampled for exposure age dating (samples 1–6 and 7–9 in Tables 1 and 2). 10

Be terrestrial cosmogenic nuclide (TCN) surface exposure dating

A total of 21 samples was collected from five moraines ranging in altitude between 2100 and 2500 m asl. Most samples were obtained from glacial boulders but in one case an ice-overridden smooth bedrock surface was also sampled (Fig. 4). The rationale behind the selection of dating samples was to establish a chronological framework for successive glacial events in the study area. This involved the targeting of ice positions representative of the largest local ice extent (i.e. furthest downvalley terminal and highest lateral moraines) and various retreat moraines (Fig. 5). Boulders were selected following procedures described by Gosse and Philips (2001) with special consideration given to boulder size, height of the sampled surface above the surrounding ground, and local geomorphic context. Only large boulders (min. diameter 1.0 m) were sampled, while blocks in potentially unstable surface positions (e.g. on slopes N10°) or near erosional features (channels, gullies etc.) were avoided altogether. Boulder lithologies in the study area are dominated by Devonian granites (granodiorite and tonalite) with a quartz content between 15 and 35%. Samples were obtained by chiselling off a 4–5 cm thick piece of rock from the top of the bedrock/boulder surface (1.5–2 kg of rock material per sample) with three to six cosmogenic samples taken from each moraine. Data recorded in the field include grid position, altitude, boulder dimensions, sample thickness and horizon shielding. Sample details are given in Table 1. Laboratory processing of rock samples into targets for Accelerator Mass Spectrometry (AMS) was carried out at ANSTO (Australia), following procedures described by Child et al. (2000) and revised in Mifsud et al. (2012). Instead of selective hydrofluoric acid etching to separate

quartz (Kohl and Nishiizumi, 1992), we repeatedly treated the samples with ortho-phosphoric acid (85% w/w H3PO4) at 250 °C to remove nonquartz mineral species, followed by a final single cycle of HF (2%) etching (Mifsud et al., 2012; Talvite, 1951). After quartz dissolution in 50% w/w HF and addition of a 9Be carrier (spike solution prepared from beryl crystal dissolved and purified with a measured 9Be concentration of 1080 ± 21 ppm), all samples were carefully fumed with the addition of 5 ml of HClO4. Dowex anion and cation resins (1X-8 and 50 W-X8) were used for ion chromatography separation to eliminate matrix contaminations (Fe, Ca, Ti etc.). Following pH-adjustment, Be(OH)2 was precipitated, dried and calcined at 800 °C. The final BeO material (0.4–0.9 mg) was mixed with a Nb binder (BeO/Nb ratio = 1:4) and then pressed into target cathodes for AMS analysis. Measurements of 10Be were made using the 10MV FN Tandem ANTARES AMS Facility (ANSTO) operating at a terminal voltage of 6.88 MV (Fink and Smith, 2007). Multiple AMS measurements of individual samples were combined as weighted means with the larger of the mean standard error of repeat 10Be/9Be values and the total statistical error. Fully blank corrected Beryllium radio-isotope ratios (full chemistry processing blank was 10Be/9Be = 2.5 ± 0.5 × 10−15) were converted to exposure ages using the CRONUS-Earth online calculator (Version 2.2), based on a reference sea-level high latitude 10Be production rate for the spallation of 4.43 ± 0.52 atoms g− 1 yr− 1 referenced to Dunai scaling (Balco, 2009). The production rate was scaled to the geographic sample location using different scaling schemes (Desilets and Zreda, 2003; Desilets et al., 2006; Dunai, 2001; Lal, 1991; Lifton et al., 2005; Stone, 2000) with all resulting ages displayed in Table 2. Additional corrections were made for individual sample thickness (using Λ

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Figure 4. Examples of glacially transported boulders sampled for in-situ cosmogenic nuclide dating. (A) Granitic blocks resting on a terminal moraine ridge with person for scale on sample MON-D-II-I. The large boulder shown in (B) is located on a proglacial outwash surface in front of the moraine shown in (A). Because of the possibility of glaciofluvial reworking this block was rejected as a sample. The image in (C) shows boulder MON-D-I-III on Shuvuun Hill, an elevated bedrock surface approximately 80 m above the valley floor. (D) View of perched moraine with a glacial block from which sample MON-E-I-II was obtained. This moraine was deposited by a distributary ice lobe which advanced from the trunk valley onto a highlying saddle near Haryn Nuur during the local glacial maximum (ice flow from right to left).

= 150 g/cm2 and ρ = 2.6 g/cm3) and local horizon shielding of cosmic rays. For the latter an azimuthal flux exponent of m = 2.65 (Masarik and Weiler, 2003) was used yielding sample dependent correction factors between 0.998 and 1.000. Further adjustments to account for potential surface erosion since the start of exposition may be considered, but correcting for these effects is difficult, as we have no reliable data on long-term erosion rates for granite lithologies in the given geographical and climatological settings. Therefore, we choose to report erosionuncorrected ages but note that had we included an (assumed) erosion rate of 1–2 mm/ka, the reported ages would increase by 2–3%. Results Late Pleistocene glaciers in the Otgon Tenger area drained dominantly in a westward direction via the Arshaan, Baga-Bogdyn and Bogdyn Valleys (Fig. 5A). High-lying glacial trimlines and ice confluence saddles are evidence for a substantial volume of ice, indicating a former system of interconnected valley glaciers (transection glaciers). Some of the outlet glaciers reached up to 40 km in length. Glacial landforms are preserved over a considerable down-valley distance and altitudinal range, allowing for the differentiation of several glacial landform associations. Each association comprises till deposits, moraine remnants and glaciofluvial drainage networks, interpreted to have formed together during a glacial advance. The most extensive ice advance is recorded through moraines on a high saddle near Haryn Nuur (250 m above valley floor; Fig. 5B) and numerous glacial boulders left on an ice-

overridden bedrock knob (Shuvuun Hill) located ~ 5 km downstream of the confluence between the Arshaan and Bogdyn Rivers (Fig. 5C; see also panorama in Fig. 6A). Subsequent ice advances were less extensive but produced prominent cross-valley terminal and stacked lateral moraines preserved upvalley of Shuvuun Hill. This zone comprises extensive hummocky terrain with multiple lobate ridges and glaciofluvial drainage channels, indicating formation by an oscillatory ice margin. We present 21 10Be exposure ages obtained from glacial boulders and striated bedrock surfaces associated with five moraine positions. Age determinations derived via different scaling models are compared in Table 2, with ages calculated using the Dunai (2001) scaling protocol discussed in the text. Based on multiple boulder ages from each site, we calculate average moraine ages expressed as the arithmetic mean of all site samples (excluding outliers) reported with the mean standard error (Table 2, column L). Among the 21 calculated 10Be-ages, we identify several samples as clear outliers (being N 3σ deviant from their mean site age): the high boulder age for sample 3 (29.9 ka compared to the site arithmetic mean of 16.2 ka) is most likely affected by cosmogenic isotope inheritance, and sample 14, which gave an age far too young (20.3 ka compared to the site mean of 38.4 ka), presumably due to enhanced erosion (spalling), post-depositional block rotation or exhumation during moraine degradation. In addition, some boulder ages from sample group 16–21 may be considered as outliers with samples 18/20 being far younger and samples 17/19 being far older than the site mean age.

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Figure 5. Topographic context and geomorphological map of the Arshaan, Baga Bogdyn and Bogdyn Valleys in the Otgon Tenger study area: the shaded relief map in (A) shows the generalized ice flow routes of major local valley glaciers. Inset rectangles denote regions of sampled moraines shown in (B) and (C/D). The sites selected for 10Be exposure dating are indicated by numbered black circles and comprise from three to six boulders per site. The resulting age chronology indicates multiple ice incursions between late MIS-3 and the Late Glacial period.

Table 1 Field information from glacially transported boulders and an ice overridden bedrock surface sampled for 10Be cosmogenic exposure age dating. No.

sample name

Latitude (°N)

Longitude (°E)

Altitude (m asl)

Boulder size (L × W × H in m)

Sample thickness (cm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

MON-D-II-I MON-D-II-II MON-D-II-III MON-D-IV-I MON-D-IV-II MON-D-IV-III MON-F-I-I MON-F-I-II MON-F-I-IV MON-E-III-I MON-E-III-II MON-E-III-III MON-D-I-I MON-D-I-II MON-D-I-III MON-E-I-I MON-E-I-II MON-E-I-III MON-E-II-I MON-E-II-II MON-E-II-III

47.6789° 47.6791° 47.6780° 47.6883° 47.6881° 47.6881° 47.6699° 47.6698° 47.6734° 47.7147° 47.7153° 47.7164° 47.6835° 47.6837° 47.6836° 47.8498° 47.8598° 47.8597° 47.8595° 47.8587° 47.8584°

97.2083° 97.2084° 97.2097° 97.2496° 97.2500° 97.2505° 97.2618° 97.2618° 97.2723° 97.2808° 97.2815° 97.2824° 97.2098° 97.2099° 97.2098° 97.3333° 97.3334° 97.3336° 97.3159° 97.3199° 97.3217°

2084 2082 2094 2150 2150 2151 2243 2272 2300 2269 2274 2277 2140 2133 2137 2568 2563 2560 2580 2596 2600

1.5 × 1.0 × 1.2 1.2 × 1.2 × 1.0 3.0 × 1.5 × 1.4 4.0 × 2.5 × 1.8 1.2 × 1.2 × 1.2 1.3 × 1.4 × 1.2 0.7 × 0.5 × 0.4 1.5 × 1.3 × 1.0 0.9 × 0.9 × 0.9 Bedrock 4.0 × 2.0 × 1.5 3.0 × 1.5 × 1.5 1.5 × 10 × 1.5 2.5 × 1.7 × 1.3 1.0 × 0.8 × 0.8 1.4 × 0.9 × 0.9 1.5 × 1.0 × 1.0 1.6 × 1.1 × 1.0 1.3 × 13 × 0.5 1.7 × 1.4 × 1.0 1.8 × 1.5 × 1.1

4.0 4.0 4.0 4.0 4.0 5.0 5.0 4.0 4.0 4.0 4.0 4.0 5.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0

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Table 2 AMS sample data, 10Be concentrations and resulting exposure ages for all Otgon Tenger moraine samples (samples 1–21). All isotopic ratios (column E) were corrected using full chemistry procedural blanks and normalized relative to NIST-4325 standard reference material using a nominal value for 10Be/9Be of 27,900 × 10−15 (Nishiizumi et al., 2007). Final analytical errors were derived from the quadrature addition of the 1σ spread in repeat measurements of AMS standards (1.0–2.0%), error in the AMS ratio, and a 1% error in Be-spike assay resulting in a combined analytical error ranging from 2.3 to 3.0% for 10Be/gquartz. Resulting exposure ages are shown for various scaling schemes (column H–K) with ages discussed in the text based on the Dunai (2001) protocol. The reported ‘site age’ (column L) is based on the arithmetic mean of all site samples with standard mean error. Samples denoted with an asterisk (*) in column K are considered to be outliers and were not included in estimating the mean moraine age. 10

Be — surface exposure age (ka)

Sample information/AMS results A

B

C

ID

No. Quartz mass (g)

D

E

9

10

10

Be (mg)

F Be/9Be (10−15)

G

H

I

MON-D-II-I MON-D-I l-l I MON-D-II-I II MON-D-IV-I MON-D-IV-II MON-D-IV-III

1 2 3 4 5 6

80.17 80.19 77.14 80.24 80.77 80.31

0.333 0.335 0.334 0.334 0.333 0.334

1284.7 1275.1 2497.0 1750.4 1530.7 1204.3

0.358 0.354 0.723 0.487 0.422 0.336

0.009 0.009 0.018 0.012 0.011 0.010

1.000 1.000 1.000 1.000 1.000 1.000

15.2 15.0 29.8 19.5 16.9 13.7

MON-F-I-I MON-F-I-II MON-F-I-IV

7 8 9

80.14 80.09 70.20

0.334 0.333 0.335

2284.8 2510.2 1834.9

0.637 ± 0.017 0.697 ± 0.018 0.585 ± 0.015

1.000 1.000 1.000

23.8 ± 2.9 25.2 ± 3.1 20.8 ± 2.5

MON-E-III-I 10 MON-E-II l-l I 11 MON-E-II l-l 11 12

61.00 79.44 70.91

0.334 0.332 0.333

1285.7 1661.2 1457.8

0.470 ± 0.013 0.465 ± 0.014 0.458 ± 0.012

1.000 1.000 1.000

MON-D-I-I MON-D-I-II MON-D-I-I 11

13 14 15

80.10 65.24 80.35

0.333 0.335 0.334

3588.1 1453.0 3350.6

0.995 ± 0.024 0.498 ± 0.012 0.931 ± 0.023

MON-E-I-I MON-E-I-II MON-E-I-I 11 MON-E-II-I MON-E-I l-l I MON-E-I l-l 11

16 17 18 19 20 21

79.28 59.86 22.64 35.91 63.40 67.26

0.333 0.333 0.334 0.334 0.334 0.334

4575.1 4758.5 967.4 3069.8 2054.8 3689.1

1.285 1.768 0.953 1.908 0.723 1.224

a b c

J

K

L

Be (106 at/g-Q) Shielding Desilets and Zreda (2003), Lifton et al. Lal (1991) Dunai Desilets et al., 2006) (2005) Stone (2000) (2001) ± ± ± ± ± ±

± ± ± ± ± ±

0.032 0.043 0.048 0.054 0.019 0.031

± ± ± ± ± ±

1.3 1.3 2.6 1.7 1.5 1.2

15.3 15.2 29.9 19.6 17.0 13.8 18.5

± ± ± ± ± ± ±

1.8 1.3 3.6* 2.4 1.5 1.7 2.2a

22.9 ± 2.4 24.2 ± 2.5 20.1 ± 2.5

23.8 ± 2.1 25.3 ± 2.2 20.8 ± 1.8

23.9 25.3 20.9 23.4

± ± ± ±

2.9 3.1 2.5 2.8a

17.2 ± 2.1 17.0 ± 2.1 16.7 ± 2.0

16.6 ± 1.7 16.4 ± 1.7 16.1 ± 1.7

17.2 ± 1.5 16.9 ± 1.5 16.7 ± 1.5

17.3 17.1 16.8 17.1

± ± ± ±

2.1 2.1 2.0 2.1a

1.000 1.000 1.000

40.0 ± 4.8 20.1 ± 2.4 37.0 ± 4.5

37.8 ± 3.9 19.4 ± 2.0 35.3 ± 3.6

39.6 ± 3.5 20.0 ± 1.8 36.9 ± 3.3

39.8 20.3 37.1 32.4

± ± ± ±

4.8 2.5* 4.5 3.9a

1.000 1.000 1.000 1.000 0.998 0.998

36.8 50.7 27.6 54.2 20.7 34.4

35.0 47.8 26.4 51.1 19.9 32.7

37.7 52.0 28.2 55.6 21.1 35.3

36.9 50.7 27.7 54.2 20.8 34.5 37.5

± ± ± ± ± ± ±

4.5 6.2 3.6 6.6 2.5 4.2 4.6

± ± ± ± ± ±

1.8 1.8 3.6 2.4 2.1 1.7

4.5 6.2 3.6 6.7 2.5 4.2

14.7 14.6 28.6 18.8 16.4 13.2

± ± ± ± ± ±

± ± ± ± ± ±

1.5 1.5 2.9 1.9 1.7 1.4

3.6 4.9 2.9 5.3 2.3 3.4

15.0 14.8 29.6 19.3 16.8 13.5

± ± ± ± ± ±

Site age (ka)

± ± ± ± ± ±

3.3 4.6 2.8 5.0 1.9 3.1

16.2 ± 1.0

23.4 ± 1.3

17.1 ± 0.2

38.4 ± 1.4

37.5 ± 5.3 (44.1 ± 4.9)b (33.0 ± 2.8)c

Arithmetic mean (outliers not excluded). Excluding samples 18 and 20. Excluding samples 17, 19, 20.

The timing of the largest ice advance is indicated by boulder ages from the distal moraine on the Haryn saddle (boulder ages of 36.9 ± 4.5 ka, 50.7 ± 6.2 ka, 27.7 ± 3.6 ka, 54.2 ± 6.6 ka, 20.8 ± 2.5 ka, and 34.5 ± 4.2 ka; samples 16–21; location shown in Fig. 5B), yielding a mean moraine age of 37.5 ± 4.6 ka (n = 6, no outliers removed). Two samples from another site, Shuvuun Hill, the bedrock knob overridden by ice in the distal portion of the Arshaan Valley, gave similar boulder ages of 39.8 ± 4.8 ka and 37.1 ± 4.5 ka (samples 13, 15), with a mean surface age of 38.4 ± 1.4 ka (n = 2). Taken together, the arithmetic mean age for all boulder ages from the two most distal ice positions is 37.7 ± 3.9 ka (n = 8). Evidence for the timing of subsequent ice advances is provided by a high lateral moraine near Saran Nuur, where three samples (dated to 23.9 ± 2.9 ka, 25.3 ± 3.1 ka and 20.9 ± 2.5 ka; samples 7, 8, 9) yielded a mean moraine age of 23.4 ± 1.3 ka (n = 3, Fig. 6B). Samples from the hummocky terminal moraine on the valley floor below yielded ages of 15.3 ± 1.8 ka, 15.2 ± 1.3 ka, 19.6 ± 2.4 ka, 17.0 ± 1.5 ka and 13.8 ± 1.7 ka (samples 1, 2, 4, 5, 6), with a mean moraine age of 16.2 ± 1.0 ka (n = 5). Two boulders associated with a low lateral moraine on the northern valley flank gave similar ages of 17.3 ± 2.1 ka and 17.1 ± 2.1 ka (samples 10, 11). This moraine is perched onto glacially striated bedrock. A sample from this bedrock surface yielded an age of 16.8 ± 2.0 ka, which matches the boulder ages from the nearby moraine and indicates that ice retreated from the moraine and bedrock surface at about the same time (mean site age 17.1 ± 0.2 ka based on samples 10, 11, 12).

Collectively, the mapping of moraines and exposure dating of glacial features at Otgon Tenger indicate several late Pleistocene phases of significant ice expansion. During each episode, glaciers reached the lower portion of the Arshaan Valley. We bracket the overall sequence into three phases of expanded glaciation, abbreviated here as OT-1, OT-2 and OT-3, occurring at 40–35 ka, ~23 ka, and 17–16 ka, respectively. Terminal moraines are not preserved in all cases, but the relative ice volume associated with each advance can be reconstructed from a combination of observations. One of the most important constraints in this assessment is provided by the exposure ages from Shuvuun Hill, showing that ice overflowed this bedrock knob only during the OT-1 advance. Although reworked glacial deposits have been found up to 5 km downstream of Shuvuun Hill, moraine landforms are not preserved in the lower valley reaches, and the precise OT-1 ice extent in the Arshaan Valley remains unclear. Following a period of glacial retreat, a subsequent ice advance is indicated by extensive terminal and lateral moraines preserved upvalley of Shuvuun Hill. Samples from a high lateral moraine (samples 7, 8, 9) on the south side of the Arshaan Valley date this advance (OT-2) to 23.4 ± 1.3 ka. Unlike the lowermost lateral moraines, the high OT-2 moraine cannot be traced into a cross-valley terminal ice position. However, moraine altitude and location (180 m above the valley floor; 4.5 km upstream from Shuvuun Hill) clearly indicate that this advance extended to a position near Shuvuun Hill. Yet it is highly improbable that the OT-2 ice overflowed Shuvuun Hill itself, as this would almost

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Figure 6. (A) A view towards the outermost preserved terminal moraine in the trunk valley from which cosmogenic dating samples 1–6 were recovered (for photographer's position see Fig. 5C). Note Shuvuun Hill, the bedrock knob to the left, with a surface positioned 80 m above valley floor. Exposure age results from glacial boulders resting on its bedrock surface indicate that this hill was overridden by ice during an earlier maximum advance (samples 13–15). The lower panel (B) shows the highest preserved lateral moraine (ca. 200 m above valley floor) from which samples 7, 8, 9 were recovered. The moraine dams off a tributary valley in which Saran Nuur formed as a consequence.

certainly have removed the glacial boulders deposited on the hilltop during the earlier OT-1 advance (samples 13 & 15). A final ice incursion into the lower Arshaan Valley (OT-3) produced the lowest set of lateral moraines and a large hummocky terminal moraine complex on the valley floor. Five samples from this moraine (samples 1, 2, 4, 5, 6) and three samples from the innermost lateral moraine on the northern valley side (samples 10, 11, 12) yielded a combined arithmetic mean of 16.5 ± 0.6 ka (n = 8), indicating a large glacier re-advance or at least the survival of a significant glacial extent until that time. Discussion Glacial history The presented surface exposure chronology from the Khangai Mountains provides the first directly dated glacial sequence from central Mongolia. All mean moraine ages fall between 37 and 16 ka, allowing for the reconstruction of ice front oscillations from late MIS-3 until well after the onset of the last termination. We identify at least two episodes of major late Pleistocene glaciation in the Otgon Tenger area: (1) a maximum ice advance (OT-1) between 40 and 35 ka during late MIS-3, and (2) a second advance phase (OT-2) at ~ 23 ka, broadly contemporaneous with the global LGM. A third and final ice advance, during the Last-Glacial–Interglacial-Transition, may be indicated by the OT-3 moraines (17–16 ka), but these limits could also be viewed as recessional moraines of the OT-2 advance. Although glaciation during the OT-1, OT-2 and OT-3 episodes was of similar magnitude, a direct comparison of the down-valley ice extent and the associated ice volume

(based on the relative valley position of terminal and lateral moraines) shows that glacial extent was largest during MIS-3 (OT-1). Instead of using arithmetic means to calculate ‘site ages’ from multiple boulder exposure ages, Heyman et al. (2011a, 2011b) argue that for exposure age groups with wide age spreads, the single oldest age from that group should be used to represent the minimum site age. Their argument is based on an analysis of over 2000 exposure ages, showing that incomplete exposure (i.e. post-depositional shielding) is the most important reason for scatter in cosmogenic exposure age data sets. Although the age spread within the Otgon Tenger data is far narrower than in Heyman et al. (2011a), it is instructive to consider which ages would be assigned to the OT-1, OT-2, and OT-3 advances using the ‘oldest age approach’. The two OT-1 moraines move from 38.4 ± 1.4 ka and 37.5 ± 5.3 ka to 39.8 ± 4.8 (based on sample 13) and 54.2 ± 6.6 ka (sample 19), respectively. This would not affect our overall conclusion of an MIS-3 age for this advance. The mean age of the OT-2 advance shifts only slightly from 23.4 ± 1.3 ka to 25.3 ± 3.1 ka, also requiring no change in our interpretation. By contrast, one of the last glacial transition moraines (samples 1–6) would move from a weighted mean of 16.2 ± 1.0 ka to 29.9 ± 3.6 ka (based on sample 3) which would effectively switch this moraine from the OT-3 to the OT-1 sequence. This, however, would still be consistent with our overall finding of a very substantial MIS-3 ice advance. Finally, our interpretation of an expanded late glacial ice extent remains unaltered, as the second OT-3 moraine (samples 10, 11, 12) moves only slightly from 17.1 ka to 17.3 ka. Overall, the presented glacial chronology from Otgon Tenger differs in several ways from the previous glacial studies in Mongolia. First, we

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find no evidence to support earlier suggestions that the largest late Pleistocene glaciation in Mongolia occurred during the coldest periods of the last glacial cycle, i.e. MIS-2 or MIS-4 (Florensov and Korzhnev, 1982; Arkhipov et al., 1986; summarized in Lehmkuhl et al., 2004). Instead, our record indicates a glacial maximum during the latter part of MIS-3, at a time of less severe cooling but increased levels of paleoprecipitation (see discussion below). Second, our finding of a substantial glacier extent in the Khangai Mountains at 16 ka, indicating a readvance or the survival of major glaciation well into the last termination, is a new feature in Mongolia's glacial record. In addition to the outlined differences, we also see similarities to other records, particularly to the results reported from the Darhad Basin (NMongolia) by Gillespie et al. (2008). Their study also suggested a significant MIS-3 ice advance, but the precision of their cosmogenic dating was limited due to probable reworking of glacial boulders, and the MIS-3 advance was proposed on a provisional basis only (see p. 181). Relying on several lines of evidence from cosmogenic, luminescence and radiocarbon dating, the same study also demonstrated that glaciers at Darhad advanced to near maximum positions at 19–17 ka, corroborating our finding of a substantial MIS-2 advance in the Otgon Tenger area. Paleoclimatic implications The results from Otgon Tenger indicate a local last glacial maximum during late MIS-3 (substage MIS-3a: 40–32 ka), coinciding with the climatic transition from interstadial to stadial conditions. Very few highresolution climate records covering this period are available from Mongolia, but data from further afield, such as the Guliya δ18O ice core record from Tibet (Thompson et al., 1997), indicate that temperatures started to decline from ~35 ka onwards (Fig. 7). This is supported by a pollen record from the Yabrai Mountains in NW-China (39°48′N/ 103°06′E), which shows that by 31–30 ka temperatures had already

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cooled by several degrees (compared to the interstadial thermal maximum), but critically, annual precipitation was still significantly higher and more evenly distributed than today (Ma et al., 1998; Wen et al., 2008). In Mongolia, there is evidence for pronounced lake highstands and a southward retreat of the Gobi desert during late MIS-3 (Feng et al., 1998,1998; Grunert et al., 2000; Komatsu et al., 2001; Walther, 1999). Lakes in the Gashun Nuur region of Inner Mongolia (Wünnemann et al., 1998) and in the ‘Valley of Great Lakes’ increased in size, while pollen records (Murad, 2011) and sedimentological proxies (Felauer, 2011) suggest comparatively wet conditions. This MIS-3a setting of a relatively cool but moist climate, probably with a greater-than-today input from winter precipitation, generated highly favorable conditions for glacial accumulation. The overall characteristics of glacial landform-sediment assemblages mapped at Otgon Tenger, suggest deposition by predominantly temperate glacier systems. We observe extensive low amplitude terminal dump moraines, numerous kame terraces, large glaciofluvial channel networks, which indicate the presence of substantial volumes of meltwater, as well as the widespread streamlining of the bedrock topography, which suggests glaciers capable of efficient basal erosion. These features are all characteristic of temperate glacier systems (Evans and Twigg, 2002) and they are consistent with the inferred regional MIS-3a climatic setting. However, the next phase of significant glacial expansion at Otgon Tenger occurred during MIS-2, which is characterized by extremely dry and cold conditions, specifically during the early part of MIS-2. This is evidenced by extreme lake low-stands in the Uvs Nuur and other lake basins (Fedotov et al., 2004; Grunert et al., 2000) and pollen data from Mongolia indicating temperature reductions of 7–15°C during winter and 1–7°C during summer, compared to modern values (Tarasov et al., 1999). In summary, we find that major late Pleistocene glaciations at Otgon Tenger occurred in response to cool-moist conditions, which dominated

Figure 7. Timing of Otgon Tenger glacial advances (A) in context of other regional and global climate paleoenvironmental proxies. (B) Normalized probability density distribution for ice advances in northern Mongolia (Darhad Basin) after Gillespie et al. (2008). (C) Stacked SPECMAP relative oxygen isotope record from planktonic foraminifera (Imbrie et al., 1984). (D) Fluctuations in δ18O in the Guliya ice core located in Qinghai-Tibet (Thompson et al., 1997). (E) Paleolake level changes of Gashun Nuur (Inner Mongolia; Wünnemann et al., 1998) and (F) Bayan Nuur (NE-Mongolia; Grunert et al., 2000). Dashed lines are placed where precise ages are uncertain. (G) Summer solar insolation at 45°N (Whitlock and Bartlein, 1997).

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during MIS-3, but also during the cold-dry setting of MIS-2. Interestingly, the presently available records from Mongolia appear to show that MIS-2 glaciers expanded both, before ~ 23 ka (this study) and after ~ 19 ka (Gillespie et al., 2008, this study) but not during the most arid part of MIS-2. The post-19 ka advance coincides with the southward retreat of the Gobi Desert (Feng et al., 1998) and an increased precipitation/evaporation balance reconstructed from Lake Hovsgol (NW-Mongolia; Murakami et al., 2010). In addition, recent work by Yamagichi and Fujita (2013) emphasizes that glacial volume may respond sensitively to seasonality changes in precipitation, even if the total amount of annual precipitation remains unaffected. Fujita (2008) found that mass balances of glaciers with strong summer-precipitationseasonality (as in Mongolia, where 80–90% of the current annual precipitation falls between May and September) are most sensitive to such seasonality changes. Suitable paleoenvironmental records that allow for the reconstruction of past seasonality patterns in Mongolia (in particular precipitation distribution) are still needed, while this issue also represents a worthwhile target for glacial modeling. Correlation to late Pleistocene glacial patterns in surrounding regions Over the recent years, paleoglaciological studies from High Asia have highlighted that the timing of late Pleistocene glacial maxima varied considerably across this vast region. Although far from being fully resolved, the available records show that a key distinction can be made between glaciers in western High Asia, which reached their maxima broadly synchronously with the MIS-2 or MIS-4 cold phases, and glaciers in the monsoon-influenced regions of Tibet, the Himalayas and eastern High Asia, which responded more strongly to climatic wet phases (Lehmkuhl and Owen, 2005; Owen et al., 2008). In some mountain regions, including the Tien Shan and Pamir, the local LGM occurred early during the last glacial cycle (MIS-4 or MIS-5), with less extensive glaciations recorded during the latter part of the cycle (e.g. Owen et al., 2012; Zech, 2012). This diminishing trend of glaciation is likely to reflect an increase in aridity in these regions, which effectively limited the potential for large glaciation over the course of the last glacial cycle. Within this framework, the glacial record from the Khangai Mountains presents a more heterogeneous signature, with major glaciation occurring during MIS-3 and also during MIS-2. Similar to the results presented here, a number of other studies from across Central Asia indicate that glaciers began a major expansion 5–10 ka before the global LGM at 22 ka, as evidenced by records from the Pamir (Abramowski et al., 2006), Tien Shan (Xu et al., 2009), Karakoram (Owen et al., 2002), southern Siberia (Back and Strecker, 1998) and the Tibetan Plateau (Lehmkuhl and Owen, 2005; Owen et al., 2003; Shi, 2002). This late MIS-3 onset of significant ice expansion corresponds to the initiation of major ice sheet growth in N-America and northern Eurasia, which began between 33 and 29 ka (Clark et al., 2009). It is clear that the regional climatic mechanisms responsible for the broadly synchronous onsets of glaciation varied from area to area, with cooling being the dominant glacial driver in some regions, and increased precipitation in others. For Mongolia, paleoecological proxy records indicate that the MIS-3 ice expansion occurred in response to moderate cooling and a simultaneous increase in relative atmospheric moisture. The broad similarities regarding the inception of late MIS-3 glacier growth across High Asia are contrasted by diverging trends during MIS-2. According to Koppes et al. (2008) and Xu et al. (2009), MIS-2 glaciers in the Tien Shan were small compared to their extent during MIS-3, MIS-4 and even MIS-5. Similar data have been reported for the Pamir (Owen et al., 2012; Röhringer et al., 2012) and the monsoon influenced regions of NE-Tibet, where MIS-2 glaciation was very limited or missing (Heyman et al., 2011a; Rother et al., 2013). This is contrasted by very large MIS-2 ice advances documented for the Russian Altai (Lehmkuhl et al., 2011; Reuther et al., 2006) and southern Siberia, where glaciation during MIS-2 reached and probably surpassed the extent of earlier glaciations (Arzhannikov et al., 2012; Lehmkuhl et al.,

2007). As we have shown, glaciers in Mongolia advanced substantially during MIS-2, but they did not reach the maximum limits set during late MIS-3. A particularly interesting feature of our record is the finding of a substantial ice advance at 17–16 ka (or the survival of extensive glaciation until that time), with these ice limits only 1–2 km distant from the LGM glacier positions. We suggest that this phase of expanded glaciation occurred in response to an intensified westerly circulation, that delivered more moisture into the region, with little or no input from the Asian Summer Monsoon, which was very weak from 32 ka onwards and would not have penetrated sufficiently northward to reach Mongolia during this time (An et al., 2012). Conclusions This paper has presented mapping results and a first exposure age chronology for moraines in the Arshaan, Baga-Bogdyn and Bogdyn Valleys (47.75°/97.25°) of the Khangai Mountains (central Mongolia). Based on these findings we draw the following conclusions: The Otgon Tenger massif (3905 m) experienced major ice advances at least three times during the last 50 ka (at 40–35 ka, ~ 23 ka, and 17–16 ka). The largest ice volume (local LGM) was reached during late MIS-3. We find no evidence that ice extent was greater at any other time during the last glacial cycle. During MIS-2, glaciers advanced to within a few kilometers of the MIS-3 limits. The OT-3 ice limits indicate a substantial ice re-advance during the last termination, or alternatively the late persistence (~16 ka) of extensive ice, in the Khangai Mountains. The overall pattern of glaciation indicates that late Pleistocene glacier systems in Mongolia responded both to increased precipitation, leading to ice advances during MIS-3 and the Late Glacial period, and also to the Northern Hemisphere induced cooling, which triggered major ice expansion during the global LGM. Acknowledgments The authors would like to thank AINSE (ANSTO) and the Deutsche Forschungsgemeinschaft (DFG: Le 730/16-1) for their financial support. We wish to express our thanks to Prof. Dr. Dorjgotov and A. Chimegsaikhan of the Mongolian Academy of Sciences (Institute of Geography) in Ulaanbaatar, as well as to the Institute's many scientists and technical staff for their support before and during the fieldwork. We thank our two reviewers for their constructive comments and Dr. Marie-Elaine van Egmond for the editing of the paper. References Abramowski, U., Bergau, A., Seebach, D., Zech, R., Glaser, B., Sosin, P., Kubik, P.W., Zech, W., 2006. Pleistocene glaciations of Central Asia: results from 10Be surface exposure ages of erratic boulders from Pamir (Tajikistan), and the Alay-Turkestan range (Kyrgyzstan). Quaternary Science Reviews 25, 1080–1096. An, Z., Colman, S.M., Zhou, W., Li, W., Brown, E.T., Jull, A.J.T., Cai, Y., Huang, Y., Lu, X., Chang, H., Song, Y., Sun, Y., Xu, H., Liu, W., Jin, Z., Liu, X., Cheng, P., Liu, Y., Ai, L., Li, X., Liu, X., Yan, L., Shi, Z., Wang, X., Wu, F., Qiang, X., Dong, J., Lu, F., Xu, X., 2012. Interplay between the Westerlies and Asian monsoon recorded in Lake Qinghai sediments since 32 ka. Scientific Reports 2, 619. http://dx.doi.org/10.1038/srep00619. Nature Publishing Group. Arkhipov, S.A., Bespaly, V.G., Faustova, M.A., Glushkova, O.Y., Isayeva, L.L., Velichko, A.A., 1986. Ice-sheet reconstructions. Quaternary Science Reviews 5, 475–482. Arzhannikov, S.G., Braucher, R., Jolivet, M., Arzhannikova, A.V., Vasallo, R., Chauvet, A., Bourlès, D., Chauvet, F., 2012. History of late Pleistocene glaciation in the central Sayan–Tuva Upland (southern Siberia). Quaternary Science Reviews 49, 16–32. Back, S., Strecker, M.R., 1998. Asymmetric late Pleistocene glaciations in the North Basin of the Baikal Rift, Russia. Journal of the Geological Society of London 155, 61–69. Balco, G., 2009. 26Al–10Be exposure age/erosion rate calculators: update from v. 2.1 to v. 2. 2. Update available on Cronus webpage under http://hess.ess.washington.edu/. Child, D., Elliot, G., Mifsud, C., Smith, A.M., Fink, D., 2000. Sample processing for Earth Science studies at ANTARES. Nuclear Instruments and Methods in Physics Research B172, 856–860. Clark, P., Dyke, A., Shakun, J., Carlson, A., Clark, J., Wohlfarth, B., Mitrovica, J., Hostetier, S., McCabe, A., 2009. The Last Glacial Maximum. Science 325, 710–714. Cunningham, W.D., 2001. Cenozoic normal faulting and regional doming in the southern Hangay region, Central Mongolia: implications for the origin of the Baikal rift province. Tectonophysics 331, 389–411.

H. Rother et al. / Quaternary Research 82 (2014) 297–308 Desilets, D., Zreda, M., 2003. Spatial and temporal distribution of secondary cosmic-ray nucleon intensities and applications to in-situ cosmogenic dating. Earth and Planetary Science Letters 206, 21–42. Desilets, D., Zreda, M., Prabu, T., 2006. Extended scaling factors for in situ cosmogenic nuclides: new measurements at low latitude. Earth and Planetary Science Letters 246, 265–276. Devyatkin, E.V., 1975. Neotectonic structures of western Mongolia (in Russian). Mesozoic and Cenozoic Tectonics and Magmatism of Mongolia. Nauka, Moscow, pp. 264–282. Dunai, T., 2001. Influence of secular variation of the geomagnetic field on production rates of in situ produced cosmogenic nuclides. Earth and Planetary Science Letters 193, 197–212. Evans, D.J.A., Twigg, D.R., 2002. The active temperate glacial landsystem: a model based on Breiðamerkurjökull and Fjallsjökull, Iceland. Quaternary Science Reviews 21, 2143–2177. Fedotov, A.P., Chebykin, E.P., Semenov, M.Y., Vorobyova, S.S., Osipov, E.Y., Golobokova, L.P., Pogodaeva, T.V., Zheleznyakova, T.O., Grachev, M.A., Tomurhuu, D., Oyunchimeg, T., Narantsetseg, T., Tomurtogoo, O., Dolgikh, P.T., Arsenyuk, M.I., De Baptist, M., 2004. Changes in the volume and salinity of Lake Khubsugul (Mongolia) in response to global climate change in the upper Pleistocene and Holocene. Palaeogeogr. Palaeoclimatol. Palaeecolo. 209, 245–257. Felauer, T., 2011. Jungquartäre Landschafts- und Klimageschichte der Südmongolei. Dissertation (in German). University Aachen (RWTH), School of Georessources and Material Technology, (Available online: http://darwin.bth.rwth-aachen.de/opus3/ volltexte/2011/3666/.). Feng, Z.-D., Chen, F.H., Tang, L.-Y., Kang, J.-C., 1998. East Asian monsoon climates and Gobi dynamics in marine isotope stages 4 and 3. Catena 33, 29–46. Fink, D., Smith, A., 2007. An inter-comparison of Be-10 and Al-26 AMS reference standards and the Be-10 half life. Nucl. Instr. and Meth. in Physics Research B 259, 600–609. Florensov, N.A., Korzhnev, S.S., 1982. Geomorphology of the Mongolian People's Republic. Joined Soviet — Mongolian geological research expeditions. Transactions, vol. 28, (Moscow (in Russian) 255 pp.). Fujita, K., 2008. Influence of precipitation seasonality on glacier mass balance and its sensitivity to climate change. Annals of Glaciology 48, 88–92. Gillespie, A.R., Burke, R.M., Komatsu, G., Bayasgalan, A., 2008. Late Pleistocene glaciers in Darhad Basin, northern Mongolia. Quaternary Research 69, 169–187. Gosse, J.C., Philips, F.M., 2001. Terrestrial in situ cosmogenic nuclides: theory and application. Quaternary Science Reviews 20, 1475–1560. Grunert, J., Lehmkuhl, F., Walther, M., 2000. Paleoclimatic evolution of the Uvs Nuur basin and adjacent areas (Western Mongolia). Quaternary International 65 (66), 171–192. Harrison, S.P., Yu, G., Tarasov, P.E., 1996. Late Quaternary lake level record from Northern Eurasia. Quaternary Research 45, 138–159. Heyman, J., Stroeven, A.P., Caffee, M., Hättestrand, C., Harbor, J.M., Li, Y., Alexanderson, H., Zhou, L., Hubbard, A., 2011a. Palaeoglaciology of Bayan Har Shan, NE Tibetan Plateau: exposure ages reveal a missing LGM expansion. Quaternary Science Reviews 30, 1988–2001. Heyman, J., Stroeven, A., Harbor, J., Caffee, M., 2011b. Too young or too old: evaluating cosmogenic exposure dating based on an analysis of compiled boulder exposure ages. Earth and Planetary Science Letters 302, 71–80. Hülle, D., Hilgers, A., Radke, U., Stolz, C., Hempelmann, N., Grunert, J., Felauer, T., Lehmkuhl, F., 2010. OSL dating of sediments from the Gobi Desert, Southern Mongolia. Quaternary Geochronology 5, 107–113. Imbrie, J., Hays, J.D., Martinson, D.G., McIntyre, A., Mix, A.C., Morley, J.J., Pisias, N.G., Prell, W.L., Shackleton, N.J., 1984. The orbital theory of Pleistocene climate: support from a revised chronology of the marine δ18O record. In: Berger, A., Imbrie, J., Hays, J., Kukla, G., Saltsman, B. (Eds.), Milankovitch and Climate, Part 1. Reidel, Boston, pp. 269–305. Kamp, U., Haserodt, K., 2004. Quaternary glaciations in the high mountains of northern Pakistan. In: Ehlers, J., Gibbard, P.L. (Eds.), Quaternary Glaciations: Extent and Chronology, Part III: South America, Asia, Africa, Australasia, Antarctica. Development in Quaternary Science, 2c. Elsevier, Amsterdam, pp. 293–311. Klinge, M., 2001. Glazialgeomorphologische Untersuchungen im mongolischen Altai als Beitrag zur jungquartären Landschafts- und Klimageschichte der Westmongolei. Aachener Geographische Arbeiten 35, 125. Kohl, C., Nishiizumi, K., 1992. Chemical isolation of quartz for measurement of in-situ produced cosmogenic nuclides. Geochimica et Cosmochimiica Acta 56, 3583–3587. Komatsu, G., Brantingham, P.J., Olsen, J., Baker, V., 2001. Paleoshoreline geomorphology of Böön Tsagaan Nuur, Tsagaan Nuur and Orog Nuur: the Valley of Lakes, Mongolia. Geomorphology 39, 83–98. Koppes, M., Gillespie, A.R., Burke, R.M., Thompson, S.C., Stone, J., 2008. Late Quaternary glaciation in the Kyrgyz Tien Shan. Quaternary Science Reviews 27, 846–866. Kurita, N., Numagutti, A., Sugimorto, A., Ichiyanagi, K., Yoshida, N., 2003. Relationship between the variation of isotopic ratios and the source of summer precipitation in eastern Siberia. Journal of Geophysical Research Atmosphere 108. http://dx.doi.org/ 10.1029/2001JD001359 (D11) (AAC 5-1, CiteID 4339). Lal, D., 1991. Cosmic ray labeling of erosion surfaces: in situ nuclide production rates and erosion models. Earth and Planetary Science Letters 104, 424–439. Lehmkuhl, F., 1997. The spatial distribution of loess and loess-like sediments in the mountain areas of Central and High Asia. Zeitschrift für Geomorphologie 111, 97–116 (N.F., Suppl. Bd.). Lehmkuhl, F., 1998. Quaternary Glaciations in Central and Western Mongolia. In: Owen, L.A. (Ed.), Mountain Glaciations. Quaternary Proceedings, 6, pp. 153–167. Lehmkuhl, F., Lang, A., 2001. Geomorphological investigations and luminescence dating in the southern part of the Khangay and the Valley of the Gobi Lakes (Mongolia). Journal of Quaternary Science 16, 69–87.

307

Lehmkuhl, F., Haselein, F., 2000. Quaternary palaeoenvironmental change on the Tibetan Plateau and adjacent areas (Western China and Mongolia). Quaternary International 65 (66), 121–145. Lehmkuhl, F., Frechen, M., Zander, A., 2007. Luminescence chronology of fluvial and aeolian deposits in the Russian Altai (Southern Siberia). Quaternary Geochronology 2, 195–201. Lehmkuhl, F., Klinge, M., Stauch, G., 2004. The extent of Late Pleistocene glaciations in the Altai und Khangay Mountains. In: Ehlers, J., Gibbard, P.L. (Eds.), Quaternary Glaciations — Extent and Chronology, Part III: South America, Asia, Africa, Australia, Antarctica. Elsevier, Oxford, pp. 243–254. Lehmkuhl, F., Klinge, M., Stauch, G., 2011. The extent and timing of Late Pleistocene Glaciations in the Altai and neighboring mountain systems. In: Ehlers, J., Gibbard, P.L., Hughes, P.D. (Eds.), Developments in Quaternary Science — Extent and Chronology — A Closer Look, vol. 15, pp. 967–979. Lehmkuhl, F., Owen, L.A., 2005. Late Quaternary glaciation of Tibet and the bordering mountains: a review. Boreas 34, 87–100. Lifton, N.A., Bieber, J.W., Clem, J.M., Duldig, M.L., Evenson, P., Humble, J.E., Pyle, R., 2005. Addressing solar modulation and long-term uncertainties in scaling in situ cosmogenic nuclide production rates. Earth and Planetary Science Letters 239, 140–161. Ma, Y.Z., Zhang, H.C., Li, J.J., Pachur, H.J., Wünnemann, B., 1998. The evolution of the palynoflora and climatic environment during the late Pleistocene in the Tennger Desert, China. Acta Botanica Sinica 40, 871–879. Masarik, J., Weiler, R., 2003. Production rates of cosmogenic nuclides in boulders. Earth and Planetary Science Letters 216, 201–208. Mifsud, C., Fujioka, T., Fink, D., 2012. Extraction and purification of quartz in rock using hot-phosphoric acid for in situ cosmogenic exposure dating. Nuclear Instruments and Methods (Series B) 294, 203–207. Murad, W., 2011. Late Quaternary Vegetation History and Climate Change in the Gobi Desert, Southern Mongolia. PhD thesis, Göttingen University. Murakami, T., Katsuta, N., Yamamoto, K., Takamatsu, Takano, M., Oda, T., Matsumoto, G., Horiuchi, K., Kawai, T., 2010. A 27-kyr record of environmental change in central Asia inferred from the sediment record of Lake Hovsgol, northwest Mongolia. Journal of Paleolimnology 43, 369–383. Nishiizumi, K., Imamura, M., Caffee, M., Southon, J., Finkel, R., McAnich, J., 2007. Absolute calibration of 10Be AMS standards. Nuclear Instruments and Methods in Physics Research B 258, 403–413. Owen, L.A., Windley, B.F., Cunningham, W.D., Badamgarov, J., Dorjnamjaa, D., 1997. Quaternary alluvial fans in the Gobi Desert, southern Mongolia: evidence for neotectonics and climate change. Journal of Quaternary Science 12, 239–252. Owen, L.A., Richards, B., Rhodes, E.J., Cunningham, W.D., Windley, B.F., Badamgarav, J., Dorjnamajaa, D., 1998. Relic permafrost structures in the Gobi of Mongolia: age and significance. Journal of Quaternary Science 13, 539–547. Owen, L.A., Finkel, R.C., Caffee, M.W., Gualtieri, L., 2002. Timing of multiple glaciations during the Late Quaternary in the Hunza Valley, Karakoram Mountains, Northern Pakistan: defined by cosmogenic radionuclide dating of moraines. Geological Society of America Bulletin 114, 593–604. Owen, L.A., Finkel, R.C., Ma, H., Spencer, J.Q., Derbyshire, E., Barnard, P.L., Caffee, M.W., 2003. Timing and style of glaciation in NE Tibet. Geological Society of America Bulletin 115, 1356–1364. Owen, L.A., Caffee, M.W., Finkel, R.C., Deong, Y.B., 2008. Quaternary glaciation of the Himalayan–Tibetan orogen. Journal of Quaternary Science 23, 513–531. Owen, L.A., Chen, J., Hedrick, K.A., Caffee, M.W., Robinson, A.C., Schoenbohm, L.M., Yuan, Z., Li, W., Imrecke, D.B., Liu, J., 2012. Quaternary glaciation of the Taskurgan Valley, Southeast Pamir. Quaternary Science Reviews 47, 56–72. Pachur, H.-J., Wünnemann, B., Zhang, H., 1995. Lake evolution in the Tengger Desert, Northwestern China, during the last 40,000 years. Quaternary Research 44, 171–180. Reuther, A.U., Herget, J., Ivy-Ochs, S., Borodavko, P., Kubik, P.W., Heine, K., 2006. Constraining the timing of the most recent cataclysmic flood event from icedammed lakes in the Russian Altai Mountains, Siberia, using cosmogenic in situ 10 Be. Geology 34, 913–916. Röhringer, I., Zech, R., Abramowski, U., Sosin, P., Aldahan, A., Kubik, P.W., Zöller, L., Zech, W., 2012. The late Pleistocene glaciation in the Bogchigir Valleys (Pamir, Tajikistan) based on 10Be surface exposure dating. Quaternary Research 78, 590–597. Rother, H., Lehmkuhl, F., Stauch, G., Freeman, S., Davidson, A., 2013. A New Surface Exposure Age Chronology from the Eastern Kunlun Shan (Lake Donggi Cona Catchment, NE-Tibet): Early Last Glacial Ice Maxima and the ‘Missing’ LGM. European Geoscience Union, (2013, Abstract.). Schlütz, F., Dulamsuren, C., Wieckowska, M., Mühlenberg, M., Hauck, M., 2008. Late Holocene vegetation history suggests natural origin of steppes in the northern Mongolian mountain taiga. Palaeogeography, Palaeoclimatology, Palaeoecology 261, 203–217. Shi, Y., 2002. Characteristics of late Quaternary monsoonal glaciation on the Tibetan Plateau and in East Asia. Quaternary International 97–98, 79–91. Stone, J.O., 2000. Air pressure and cosmogenic isotope production. Journal of Geophysical Research 105, 23753–23759. Sun, Q., Wang, S., Zhou, J., Shen, J., Cheng, P., Xie, X., Wu, F., 2009. Lake surface fluctuations since the late deglaciation at Lake Daihai, North central China: a direct indicator of hydrological process response to East Asian monsoon climate. Quaternary International 194, 45–54. Talvite, N.A., 1951. Determination of quartz in presence of silicates using phosphoric acid. Analytical Chemistry 23, 623–626. Tarasov, P.E., Peyron, O., Guiot, J., Brewer, S., Volkova, V.S., Bezusko, L.G., Dorofeyuk, N.I., Kvavadze, E.V., Osipova, I.M., Panova, N.K., 1999. Last Glacial Maximum climate of the former Soviet Union and Mongolia reconstructed from pollen and plant macrofossil data. Climate Dynamics 15, 227–240.

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H. Rother et al. / Quaternary Research 82 (2014) 297–308

Thompson, L.G., Yao, T., Davis, M.E., Henderson, K.A., Mosley-Thompson, E., Lin, P.-N., Beer, J., Synal, H.A., Cole-Dai, J., Bolzan, J.F., 1997. Tropical climate instability: the last glacial cycle from Quinghai-Tibetan ice core. Science 276, 1821–1825. Walther, M., 1999. Befunde zur Seespiegel- und Klimaentwicklung in der NordwestMongolei. Die Erde 130, 131–150. Watanabe, T., Nakamura, T., Watanabe Nara, F., Kakegawa, T., Horiuchi, K., Senda, R., Oda, T., Nishimura, M., Matsumoto, G.I., Kawai, T., 2009. High-time resolution AMS 14C data sets for Lake Baikal and Lake Hovsgol sediment cores: changes in radiocarbon age and sedimentation rates during the transition from the Last Glacial to the Holocene. Quaternary International 205, 12–20. Wen, X., Li, B., Zheng, Y., Zhang, D.D., Ye, J., 2008. Climate variability in the Salawusu River valley of the Ordos Plateau (Inner Mongolia, China) during Marine Isotope Stage 3. Journal of Quaternary Science 24, 61–74. Whitlock, C., Bartlein, P., 1997. Vegetation and climate change in northwest America during the past 125 kyr. Nature 388, 57–61.

Wünnemann, B., Pachur, H.-J., Li, J., Zhang, H., 1998. Chronologie der pleistozänen und holozänen Seespiegelschwankungen des Gaxun Nur/Sogo Nur und Baijian Hu, Innere Mongolei, NW-China. Petermanns Geographische Mitteilungen 142, 191–206. Xu, X., Kleidon, A., Miller, L., Wang, S., Wang, L., Dong, G., 2009. Late Quaternary glaciation in the Tianshan and implications for palaeoclimatic change: a review. Boreas 39, 215–232. Yamagichi, S., Fujita, K., 2013. Modeling glacier behavior under different precipitation seasonalities. Arctic Antarctic and Alpine Research 45, 143–152. Yang, X., Rost, K.T., Lehmkuhl, F., Zhenda, Z., Dodson, J., 2004. The evolution of dry lands in northern China and in the Republic of Mongolia since the Last Glacial Maximum. Quaternary International 118 (119), 69–85. Zech, R., 2012. A late Pleistocene glacial chronology from the Kitschi–Kurumdu Valley, Tien Shan (Kyrgyzstan), based on 10Be surface exposure dating. Quaternary Research 77, 281–288. Zorin, Y.A., 1999. Geodynamics of the western part of the Mongolia Okhotsk collisional belt, Trans-Baikal region (Russia) and Mongolia. Tectonophysics 306, 33–56.